Phase tracking reference signal for sub-symbol phase tracking

ABSTRACT

Methods, systems, and devices for wireless communications are described for phase error estimation and correction with sub-symbol resolution. A transmitting device may precode symbols (e.g., phase tracking reference signal (PT-RS) symbols) using a discrete Fourier transform (DFT). The transmitting device may map the DFT-precoded symbols to sets of adjacent subcarriers of a wireless signal, and may map other symbols to other subcarriers of the wireless signal. A receiving device may receive the wireless signal and may compare time domain representations of the DFT-precoded symbols with time domain representations of known reference symbols. The receiving device may estimate a phase error with sub-symbol resolution in the time domain based at least in part on the comparison, and may apply a phase correction in either the time or frequency domain to the other symbols.

CROSS REFERENCES

The present application for patent claims the benefit of U.S.Provisional Patent Application No. 62/597,833 by BAI, et al., entitled“PHASE TRACKING REFERENCE SIGNAL FOR SUB-SYMBOL PHASE TRACKING,” filedDec. 12, 2017, assigned to the assignee hereof, and expresslyincorporated herein.

BACKGROUND

The following relates generally to wireless communication, and morespecifically to phase tracking reference signal for sub-symbol phasetracking.

Wireless communications systems are widely deployed to provide varioustypes of communication content such as voice, video, packet data,messaging, broadcast, and so on. These systems may be capable ofsupporting communication with multiple users by sharing the availablesystem resources (e.g., time, frequency, and power). Examples of suchmultiple-access systems include fourth generation (4G) systems such asLong Term Evolution (LTE) systems, LTE-Advanced (LTE-A) systems, orLTE-A Pro systems, and fifth generation (5G) systems which may bereferred to as New Radio (NR) systems. These systems may employtechnologies such as code division multiple access (CDMA), time divisionmultiple access (TDMA), frequency division multiple access (FDMA),orthogonal frequency division multiple access (OFDMA), or discreteFourier transform-spread-OFDM (DFT-S-OFDM). A wireless multiple-accesscommunications system may include a number of base stations or networkaccess nodes, each simultaneously supporting communication for multiplecommunication devices, which may be otherwise known as user equipment(UE).

SUMMARY

The described techniques relate to improved methods, systems, devices,or apparatuses that support a phase tracking reference signal forsub-symbol phase tracking. Generally, the described techniques providefor phase error estimation and correction with sub-symbol resolution.

A transmitting device, such as a base station, may use a discreteFourier transform (DFT) to precode one or more sets of symbols and maymap the resulting sets of DFT-precoded symbols to corresponding sets ofsubcarriers that are adjacent in frequency. The transmitting device mayalso frequency division multiplex the DFT-precoded symbols with othersymbols (e.g., non-DFT-precoded symbols) by mapping the other symbols toother subcarriers. A user equipment (UE) (or other receiving device,such as another base station) may receive a wireless signal thatincludes the subcarriers, and thus may receive the DFT-precoded symbolsas well as the other symbols. The UE may estimate a phase error based atleast in part on the DFT-precoded symbols. For example, the UE mayestimate the phase error based at least in part on a comparison of timedomain representations of the DFT-precoded symbols with time domainrepresentations of corresponding reference symbols, which may supportphase error estimation with sub-symbol resolution in the time domain.The UE may apply a phase error correction to the other symbols based atleast in part on the estimated phase error. In some cases, theDFT-precoded symbols may be phase tracking reference signal (PT-RS)symbols.

A method of wireless communication is described. The method may includedetermining a DFT configuration for a plurality of symbols, generating,based at least in part on the DFT configuration, a plurality ofDFT-precoded symbols corresponding to the plurality of symbols, mappingthe plurality of DFT-precoded symbols to a corresponding plurality ofsubcarriers, the plurality of subcarriers including at least a subset ofsubcarriers that are adjacent in frequency, mapping additional symbolsto additional subcarriers, and transmitting the plurality ofDFT-precoded symbols via a wireless signal that includes the pluralityof subcarriers and the additional subcarriers.

An apparatus for wireless communication is described. The apparatus mayinclude means for determining a DFT configuration for a plurality ofsymbols, means for generating, based at least in part on the DFTconfiguration, a plurality of DFT-precoded symbols corresponding to theplurality of symbols, means for mapping the plurality of DFT-precodedsymbols to a corresponding plurality of subcarriers, the plurality ofsubcarriers including at least a subset of subcarriers that are adjacentin frequency, means for mapping additional symbols to additionalsubcarriers, and means for transmitting the plurality of DFT-precodedsymbols via a wireless signal that includes the plurality of subcarriersand the additional subcarriers.

Another apparatus for wireless communication is described. The apparatusmay include a processor, memory in electronic communication with theprocessor, and instructions stored in the memory. The instructions maybe operable to cause the processor to determine a DFT configuration fora plurality of symbols, generate, based at least in part on the DFTconfiguration, a plurality of DFT-precoded symbols corresponding to theplurality of symbols, map the plurality of DFT-precoded symbols to acorresponding plurality of subcarriers, the plurality of subcarriersincluding at least a subset of subcarriers that are adjacent infrequency, map additional symbols to additional subcarriers, andtransmit the plurality of DFT-precoded symbols via a wireless signalthat includes the plurality of subcarriers and the additionalsubcarriers.

A non-transitory computer-readable medium for wireless communication isdescribed. The non-transitory computer-readable medium may includeinstructions operable to cause a processor to determine a DFTconfiguration for a plurality of symbols, generate, based at least inpart on the DFT configuration, a plurality of DFT-precoded symbolscorresponding to the plurality of symbols, map the plurality ofDFT-precoded symbols to a corresponding plurality of subcarriers, theplurality of subcarriers including at least a subset of subcarriers thatare adjacent in frequency, map additional symbols to additionalsubcarriers, and transmit the plurality of DFT-precoded symbols via awireless signal that includes the plurality of subcarriers and theadditional subcarriers.

Some examples of the method, apparatus, and non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for mapping at least one of theadditional symbols to a subcarrier within the wireless signal that maybe interposed in frequency between two of the plurality of subcarriers.

In some examples of the method, apparatus, and non-transitorycomputer-readable medium described above, generating the plurality ofDFT-precoded symbols comprises generating a first subset of theplurality of DFT-precoded symbols using a first DFT precoding unit.

In some examples of the method, apparatus, and non-transitorycomputer-readable medium described above, mapping the plurality ofDFT-precoded symbols to the plurality of subcarriers comprises mappingthe first subset of the plurality of DFT-precoded symbols to the subsetof subcarriers that may be adjacent in frequency.

In some examples of the method, apparatus, and non-transitorycomputer-readable medium described above, mapping the plurality ofDFT-precoded symbols to the plurality of subcarriers comprises mappingsubsets of the plurality of DFT-precoded symbols to respective subsetsof the plurality of subcarriers, wherein each subset of the plurality ofDFT-precoded symbols may be associated with a respective DFT precodingunit, and wherein each respective subset of the plurality of subcarrierscomprises subcarriers that may be adjacent in frequency.

In some examples of the method, apparatus, and non-transitorycomputer-readable medium described above, generating the plurality ofDFT-precoded symbols comprises accessing a lookup table that associatesthe plurality of symbols with the plurality of DFT-precoded symbolsbased at least in part on the DFT configuration. Some examples of themethod, apparatus, and non-transitory computer-readable medium describedabove may further include processes, features, means, or instructionsfor retrieving the plurality of DFT-precoded symbols from memory.

Some examples of the method, apparatus, and non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for receiving, from a wireless device,channel quality information or signals to assist in determining channelquality information. Some examples of the method, apparatus, andnon-transitory computer-readable medium described above may furtherinclude processes, features, means, or instructions for determining,based at least in part on the channel quality information, at least oneof the plurality of subcarriers.

In some examples of the method, apparatus, and non-transitorycomputer-readable medium described above, the channel qualityinformation comprises a signal-to-noise ratio (SNR) for at least one ofthe plurality of subcarriers.

Some examples of the method, apparatus, and non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for receiving, from a wireless device,an indication of one or more preferred subcarriers. Some examples of themethod, apparatus, and non-transitory computer-readable medium describedabove may further include processes, features, means, or instructionsfor determining, based at least in part on the indication, at least oneof the plurality of subcarriers.

In some examples of the method, apparatus, and non-transitorycomputer-readable medium described above, determining the DFTconfiguration comprises determining a number of DFT precoding units anda size of each DFT precoding unit.

In some examples of the method, apparatus, and non-transitorycomputer-readable medium described above, determining the DFTconfiguration comprises determining the DFT configuration based at leastin part on a modulation and coding scheme (MCS), an SNR of at least oneof the plurality of subcarriers, a phase noise associated with at leastone of the plurality of subcarriers, a carrier frequency offset (CFO)associated with at least one of the plurality of subcarriers, or anycombination thereof.

Some examples of the method, apparatus, and non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for transmitting an indication of theDFT configuration, an indication of the plurality of subcarriers, or anycombination thereof.

In some examples of the method, apparatus, and non-transitorycomputer-readable medium described above, the plurality of symbolscomprises a plurality of PT-RS symbols.

In some examples of the method, apparatus, and non-transitorycomputer-readable medium described above, each of the plurality of PT-RSsymbols corresponds to a distinct PT-RS sequence.

A method of wireless communication is described. The method may includeidentifying a DFT configuration for a plurality of DFT-precoded symbols,receiving the plurality of DFT-precoded symbols via a correspondingplurality of subcarriers within a wireless signal and additional symbolsvia additional subcarriers within the wireless signal, the plurality ofsubcarriers including at least a subset of subcarriers that are adjacentin frequency, estimating a phase error based at least in part on theplurality of DFT-precoded symbols and the DFT configuration, andapplying a phase correction based at least in part on the phase error tothe additional symbols.

An apparatus for wireless communication is described. The apparatus mayinclude means for identifying a DFT configuration for a plurality ofDFT-precoded symbols, means for receiving the plurality of DFT-precodedsymbols via a corresponding plurality of subcarriers within a wirelesssignal and additional symbols via additional subcarriers within thewireless signal, the plurality of subcarriers including at least asubset of subcarriers that are adjacent in frequency, means forestimating a phase error based at least in part on the plurality ofDFT-precoded symbols and the DFT configuration, and means for applying aphase correction based at least in part on the phase error to theadditional symbols.

Another apparatus for wireless communication is described. The apparatusmay include a processor, memory in electronic communication with theprocessor, and instructions stored in the memory. The instructions maybe operable to cause the processor to identify a DFT configuration for aplurality of DFT-precoded symbols, receive the plurality of DFT-precodedsymbols via a corresponding plurality of subcarriers within a wirelesssignal and additional symbols via additional subcarriers within thewireless signal, the plurality of subcarriers including at least asubset of subcarriers that are adjacent in frequency, estimate a phaseerror based at least in part on the plurality of DFT-precoded symbolsand the DFT configuration, and apply a phase correction based at leastin part on the phase error to the additional symbols.

A non-transitory computer-readable medium for wireless communication isdescribed. The non-transitory computer-readable medium may includeinstructions operable to cause a processor to identify a DFTconfiguration for a plurality of DFT-precoded symbols, receive theplurality of DFT-precoded symbols via a corresponding plurality ofsubcarriers within a wireless signal and additional symbols viaadditional subcarriers within the wireless signal, the plurality ofsubcarriers including at least a subset of subcarriers that are adjacentin frequency, estimate a phase error based at least in part on theplurality of DFT-precoded symbols and the DFT configuration, and apply aphase correction based at least in part on the phase error to theadditional symbols.

Some examples of the method, apparatus, and non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for processing the plurality ofDFT-precoded symbols based at least in part on the DFT configuration toobtain a corresponding plurality of symbols.

In some examples of the method, apparatus, and non-transitorycomputer-readable medium described above, estimating the phase errorcomprises comparing the plurality of symbols to a correspondingplurality of reference symbols in the time domain.

Some examples of the method, apparatus, and non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for receiving an indication of theplurality of reference symbols.

In some examples of the method, apparatus, and non-transitorycomputer-readable medium described above, estimating the phase errorfurther comprises computing a phase error trajectory for at least one ofthe plurality of subcarriers.

In some examples of the method, apparatus, and non-transitorycomputer-readable medium described above, processing the plurality ofDFT-precoded symbols comprises applying an inverse DFT (IDFT) to theplurality of DFT-precoded symbols.

In some examples of the method, apparatus, and non-transitorycomputer-readable medium described above, processing the plurality ofDFT-precoded symbols comprises accessing a lookup table that associatesthe plurality of symbols with the plurality of DFT-precoded symbolsbased at least in part on the DFT configuration. Some examples of themethod, apparatus, and non-transitory computer-readable medium describedabove may further include processes, features, means, or instructionsfor retrieving the plurality of symbols from memory.

Some examples of the method, apparatus, and non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for transmitting an indication of apreferred subcarrier.

Some examples of the method, apparatus, and non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for determining the preferredsubcarrier based at least in part on an SNR.

Some examples of the method, apparatus, and non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for transmitting an indication of apreferred DFT configuration.

In some examples of the method, apparatus, and non-transitorycomputer-readable medium described above, identifying the DFTconfiguration comprises receiving an indication of a number of DFTprecoding units and a size of each DFT precoding unit.

Some examples of the method, apparatus, and non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for receiving an indication of theplurality of subcarriers.

Some examples of the method, apparatus, and non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for applying the phase correctionoccurs in either the time domain or the frequency domain.

Some examples of the method, apparatus, and non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for receiving at least one of theadditional symbols via a subcarrier within the wireless signal that maybe interposed in frequency between two of the plurality of subcarriers.

In some examples of the method, apparatus, and non-transitorycomputer-readable medium described above, receiving the plurality ofDFT-precoded symbols comprises receiving subsets of the plurality ofDFT-precoded symbols via respective subsets of the plurality ofsubcarriers, each subset of the plurality of DFT-precoded symbolsassociated with a respective DFT precoding unit, and each respectivesubset of the plurality of subcarriers comprising subcarriers that maybe adjacent in frequency.

In some examples of the method, apparatus, and non-transitorycomputer-readable medium described above, the plurality of symbolscomprises a plurality of PT-RS symbols.

In some examples of the method, apparatus, and non-transitorycomputer-readable medium described above, each of the plurality ofDFT-precoded PT-RS symbols corresponds to a distinct PT-RS sequence.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example of a system for wireless communicationthat supports a phase tracking reference signal (PT-RS) for sub-symbolphase tracking in accordance with aspects of the present disclosure.

FIG. 2 illustrates an example of a system for wireless communicationthat supports a PT-RS for sub-symbol phase tracking in accordance withaspects of the present disclosure.

FIG. 3 illustrates an example of a discrete Fourier transform (DFT)precoding system that supports a PT-RS for sub-symbol phase tracking inaccordance with aspects of the present disclosure.

FIG. 4 illustrates an example of a phase error compensation system thatsupports a PT-RS for sub-symbol phase tracking in accordance withaspects of the present disclosure.

FIGS. 5 through 7 show block diagrams of a device that supports a PT-RSfor sub-symbol phase tracking in accordance with aspects of the presentdisclosure.

FIG. 8 illustrates a block diagram of a system including a base stationthat supports a PT-RS for sub-symbol phase tracking in accordance withaspects of the present disclosure.

FIGS. 9 through 11 show block diagrams of a device that supports a PT-RSfor sub-symbol phase tracking in accordance with aspects of the presentdisclosure.

FIG. 12 illustrates a block diagram of a system including a UE thatsupports a PT-RS for sub-symbol phase tracking in accordance withaspects of the present disclosure.

FIGS. 13 through 14 illustrate methods for phase tracking referencesignal for sub-symbol phase tracking in accordance with aspects of thepresent disclosure.

DETAILED DESCRIPTION

Devices in a wireless communications system, such as base stations andUEs, may communicate using electromagnetic waves of various frequencies.A transmitting device, such as a base station or UE, may modulate one ormore waveforms according to a modulation scheme, and a modulatedwaveform may be divided into time units known as symbol durations. Somemodulation schemes (e.g., phase shift keying (PSK) or quadratureamplitude modulation (QAM) schemes) may represent information based atleast in part on a phase of the modulated waveform (e.g., the phase ofthe waveform, or the phase and amplitude of the waveform), where thecharacteristics of a modulated waveform during a symbol duration may bereferred to as a symbol (or modulation symbol).

Phase errors may arise, however, due to a variety of factors. Forexample, phase errors may arise due to rapid, random fluctuations in thephase of a waveform, which be referred to as phase noise. In some cases,phase noise may be caused by jitter in an oscillator at either atransmitter or a receiver. The power of a phase noise component of awaveform, and thus the impact of phase noise, may increase as thefrequency of a waveform increases. As another example, phase errors mayarise due to carrier frequency offset (CFO), which may in some cases becaused by frequency mismatch between an oscillator at a receiver and anoscillator at a transmitter. And as another example, phase errors mayarise due to the Doppler effect, as a receiver and a transmitter maymove relative to one another. The impact of phase errors may increase asthe order of modulation increases, as the phase difference betweendistinct modulation symbols may become finer (that is, may decrease).

As described herein, wireless devices, such as base stations and UEs,may support techniques for identifying and correcting phase errors at areceiving device. A base station may use a discrete Fourier transform(DFT) to precode a set of symbols, may frequency division multiplex theDFT-precoded symbols with other symbols (e.g., non-DFT-precodedsymbols), and may transmit the frequency division multiplexed symbols toa UE via a wireless signal. At least some of the DFT-precoded symbolsmay be mapped to adjacent subcarriers (that is, adjacent frequencytones) within the wireless signal. A UE (or other receiving device, suchas another base station) may receive the wireless signal and mayestimate a phase error based at least in part on the DFT-precodedsymbols. In some cases, the DFT-precoded symbols may be carried byadjacent subcarriers, and the UE may estimate the phase error based atleast in part on a comparison of time domain representations of theDFT-precoded symbols with time domain representations of correspondingreference symbols, which may support phase error estimation withsub-symbol resolution. The UE may apply a phase error correction to theother symbols based at least in part on the estimated phase error. Insome cases, the DFT-precoded symbols may be phase tracking referencesignal (PT-RS) symbols.

Aspects of the disclosure are initially described in the context of awireless communications system. Aspects of the disclosure are furtherillustrated by and described with reference to apparatus diagrams,system diagrams, and flowcharts that relate to phase tracking referencesignal for sub-symbol phase tracking.

FIG. 1 illustrates an example of a wireless communications system 100 inaccordance with various aspects of the present disclosure. The wirelesscommunications system 100 includes base stations 105, UEs 115, and acore network 130. In some examples, the wireless communications system100 may be a Long Term Evolution (LTE) network, an LTE-Advanced (LTE-A)network, an LTE-A Pro network, or a New Radio (NR) network. In somecases, wireless communications system 100 may support enhanced broadbandcommunications, ultra-reliable (e.g., mission critical) communications,low latency communications, or communications with low-cost andlow-complexity devices.

Base stations 105 may wirelessly communicate with UEs 115 via one ormore base station antennas. Base stations 105 described herein mayinclude or may be referred to by those skilled in the art as a basetransceiver station, a radio base station, an access point, a radiotransceiver, a NodeB, an eNodeB (eNB), a next-generation Node B orgiga-nodeB (either of which may be referred to as a gNB), a Home NodeB,a Home eNodeB, or some other suitable terminology. Wirelesscommunications system 100 may include base stations 105 of differenttypes (e.g., macro or small cell base stations). The UEs 115 describedherein may be able to communicate with various types of base stations105 and network equipment including macro eNBs, small cell eNBs, gNBs,relay base stations, and the like.

Each base station 105 may be associated with a particular geographiccoverage area 110 in which communications with various UEs 115 issupported. Each base station 105 may provide communication coverage fora respective geographic coverage area 110 via communication links 125,and communication links 125 between a base station 105 and a UE 115 mayutilize one or more carriers. Communication links 125 shown in wirelesscommunications system 100 may include uplink transmissions from a UE 115to a base station 105, or downlink transmissions from a base station 105to a UE 115. Downlink transmissions may also be called forward linktransmissions while uplink transmissions may also be called reverse linktransmissions.

The geographic coverage area 110 for a base station 105 may be dividedinto sectors making up only a portion of the geographic coverage area110, and each sector may be associated with a cell. For example, eachbase station 105 may provide communication coverage for a macro cell, asmall cell, a hot spot, or other types of cells, or various combinationsthereof. In some examples, a base station 105 may be movable andtherefore provide communication coverage for a moving geographiccoverage area 110. In some examples, different geographic coverage areas110 associated with different technologies may overlap, and overlappinggeographic coverage areas 110 associated with different technologies maybe supported by the same base station 105 or by different base stations105. The wireless communications system 100 may include, for example, aheterogeneous LTE/LTE-A/LTE-A Pro or NR network in which different typesof base stations 105 provide coverage for various geographic coverageareas 110.

The term “cell” refers to a logical communication entity used forcommunication with a base station 105 (e.g., over a carrier), and may beassociated with an identifier for distinguishing neighboring cells(e.g., a physical cell identifier (PCID), a virtual cell identifier(VCID)) operating via the same or a different carrier. In some examples,a carrier may support multiple cells, and different cells may beconfigured according to different protocol types (e.g., machine-typecommunication (MTC), narrowband Internet-of-Things (NB-IoT), enhancedmobile broadband (eMBB), or others) that may provide access fordifferent types of devices. In some cases, the term “cell” may refer toa portion of a geographic coverage area 110 (e.g., a sector) over whichthe logical entity operates.

UEs 115 may be dispersed throughout the wireless communications system100, and each UE 115 may be stationary or mobile. A UE 115 may also bereferred to as a mobile device, a wireless device, a remote device, ahandheld device, or a subscriber device, or some other suitableterminology, where the “device” may also be referred to as a unit, astation, a terminal, or a client. A UE 115 may also be a personalelectronic device such as a cellular phone, a personal digital assistant(PDA), a tablet computer, a laptop computer, or a personal computer. Insome examples, a UE 115 may also refer to a wireless local loop (WLL)station, an Internet of Things (IoT) device, an Internet of Everything(IoE) device, or an MTC device, or the like, which may be implemented invarious articles such as appliances, vehicles, meters, or the like.

Some UEs 115, such as MTC or IoT devices, may be low cost or lowcomplexity devices, and may provide for automated communication betweenmachines (e.g., via Machine-to-Machine (M2M) communication). M2Mcommunication or MTC may refer to data communication technologies thatallow devices to communicate with one another or a base station 105without human intervention. In some examples, M2M communication or MTCmay include communications from devices that integrate sensors or metersto measure or capture information and relay that information to acentral server or application program that can make use of theinformation or present the information to humans interacting with theprogram or application. Some UEs 115 may be designed to collectinformation or enable automated behavior of machines. Examples ofapplications for MTC devices include smart metering, inventorymonitoring, water level monitoring, equipment monitoring, healthcaremonitoring, wildlife monitoring, weather and geological eventmonitoring, fleet management and tracking, remote security sensing,physical access control, and transaction-based business charging.

Some UEs 115 may be configured to employ operating modes that reducepower consumption, such as half-duplex communications (e.g., a mode thatsupports one-way communication via transmission or reception, but nottransmission and reception simultaneously). In some examples half-duplexcommunications may be performed at a reduced peak rate. Other powerconservation techniques for UEs 115 include entering a power saving“deep sleep” mode when not engaging in active communications, oroperating over a limited bandwidth (e.g., according to narrowbandcommunications). In some cases, UEs 115 may be designed to supportcritical functions (e.g., mission critical functions), and a wirelesscommunications system 100 may be configured to provide ultra-reliablecommunications for these functions.

In some cases, a UE 115 may also be able to communicate directly withother UEs 115 (e.g., using a peer-to-peer (P2P) or device-to-device(D2D) protocol). One or more of a group of UEs 115 utilizing D2Dcommunications may be within the geographic coverage area 110 of a basestation 105. Other UEs 115 in such a group may be outside the geographiccoverage area 110 of a base station 105, or be otherwise unable toreceive transmissions from a base station 105. In some cases, groups ofUEs 115 communicating via D2D communications may utilize a one-to-many(1:M) system in which each UE 115 transmits to every other UE 115 in thegroup. In some cases, a base station 105 facilitates the scheduling ofresources for D2D communications. In other cases, D2D communications arecarried out between UEs 115 without the involvement of a base station105.

Base stations 105 may communicate with the core network 130 and with oneanother. For example, base stations 105 may interface with the corenetwork 130 through backhaul links 132 (e.g., via an Si or otherinterface). Base stations 105 may communicate with one another overbackhaul links 134 (e.g., via an X2 or other interface) either directly(e.g., directly between base stations 105) or indirectly (e.g., via corenetwork 130).

The core network 130 may provide user authentication, accessauthorization, tracking, Internet Protocol (IP) connectivity, and otheraccess, routing, or mobility functions. The core network 130 may be anevolved packet core (EPC), which may include at least one mobilitymanagement entity (MME), at least one serving gateway (S-GW), and atleast one Packet Data Network (PDN) gateway (P-GW). The MME may managenon-access stratum (e.g., control plane) functions such as mobility,authentication, and bearer management for UEs 115 served by basestations 105 associated with the EPC. User IP packets may be transferredthrough the S-GW, which itself may be connected to the P-GW. The P-GWmay provide IP address allocation as well as other functions. The P-GWmay be connected to the network operators IP services. The operators IPservices may include access to the Internet, Intranet(s), an IPMultimedia Subsystem (IMS), or a Packet-Switched (PS) Streaming Service.

At least some of the network devices, such as a base station 105, mayinclude subcomponents such as an access network entity, which may be anexample of an access node controller (ANC). Each access network entitymay communicate with UEs 115 through a number of other access networktransmission entities, which may be referred to as a radio head, a smartradio head, or a transmission/reception point (TRP). In someconfigurations, various functions of each access network entity or basestation 105 may be distributed across various network devices (e.g.,radio heads and access network controllers) or consolidated into asingle network device (e.g., a base station 105).

Wireless communications system 100 may operate using one or morefrequency bands, typically in the range of 300 MHz to 300 GHz.Generally, the region from 300 MHz to 3 GHz is known as the ultra-highfrequency (UHF) region or decimeter band, since the wavelengths rangefrom approximately one decimeter to one meter in length. UHF waves maybe blocked or redirected by buildings and environmental features.However, the waves may penetrate structures sufficiently for a macrocell to provide service to UEs 115 located indoors. Transmission of UHFwaves may be associated with smaller antennas and shorter range (e.g.,less than 100 km) compared to transmission using the smaller frequenciesand longer waves of the high frequency (HF) or very high frequency (VHF)portion of the spectrum below 300 MHz.

Wireless communications system 100 may also operate in a super highfrequency (SHF) region using frequency bands from 3 GHz to 30 GHz, alsoknown as the centimeter band. The SHF region includes bands such as the5 GHz industrial, scientific, and medical (ISM) bands, which may be usedopportunistically by devices that can tolerate interference from otherusers.

Wireless communications system 100 may also operate in an extremely highfrequency (EHF) region of the spectrum (e.g., from 30 GHz to 300 GHz),also known as the millimeter band. In some examples, wirelesscommunications system 100 may support millimeter wave (mmW)communications between UEs 115 and base stations 105, and EHF antennasof the respective devices may be even smaller and more closely spacedthan UHF antennas. In some cases, this may facilitate use of antennaarrays within a UE 115. However, the propagation of EHF transmissionsmay be subject to even greater atmospheric attenuation and shorter rangethan SHF or UHF transmissions. Techniques disclosed herein may beemployed across transmissions that use one or more different frequencyregions, and designated use of bands across these frequency regions maydiffer by country or regulating body.

In some cases, wireless communications system 100 may utilize bothlicensed and unlicensed radio frequency spectrum bands. For example,wireless communications system 100 may employ License Assisted Access(LAA), LTE-Unlicensed (LTE-U) radio access technology, or NR technologyin an unlicensed band such as the 5 GHz ISM band. When operating inunlicensed radio frequency spectrum bands, wireless devices such as basestations 105 and UEs 115 may employ listen-before-talk (LBT) proceduresto ensure a frequency channel is clear before transmitting data. In somecases, operations in unlicensed bands may be based on a CA configurationin conjunction with CCs operating in a licensed band (e.g., LAA).Operations in unlicensed spectrum may include downlink transmissions,uplink transmissions, peer-to-peer transmissions, or a combination ofthese. Duplexing in unlicensed spectrum may be based on frequencydivision duplexing (FDD), time division duplexing (TDD), or acombination of both.

In some examples, base station 105 or UE 115 may be equipped withmultiple antennas, which may be used to employ techniques such astransmit diversity, receive diversity, multiple-input multiple-output(MIMO) communications, or beamforming. For example, wirelesscommunications system 100 may use a transmission scheme between atransmitting device (e.g., a base station 105) and a receiving device(e.g., a UE 115), where the transmitting device is equipped withmultiple antennas and the receiving devices are equipped with one ormore antennas. MIMO communications may employ multipath signalpropagation to increase the spectral efficiency by transmitting orreceiving multiple signals via different spatial layers, which may bereferred to as spatial multiplexing. The multiple signals may, forexample, be transmitted by the transmitting device via differentantennas or different combinations of antennas. Likewise, the multiplesignals may be received by the receiving device via different antennasor different combinations of antennas. Each of the multiple signals maybe referred to as a separate spatial stream, and may carry bitsassociated with the same data stream (e.g., the same codeword) ordifferent data streams. Different spatial layers may be associated withdifferent antenna ports used for channel measurement and reporting. MIMOtechniques include single-user MIMO (SU-MIMO) where multiple spatiallayers are transmitted to the same receiving device, and multiple-userMIMO (MU-MIMO) where multiple spatial layers are transmitted to multipledevices.

Beamforming, which may also be referred to as spatial filtering,directional transmission, or directional reception, is a signalprocessing technique that may be used at a transmitting device or areceiving device (e.g., a base station 105 or a UE 115) to shape orsteer an antenna beam (e.g., a transmit beam or receive beam) along aspatial path between the transmitting device and the receiving device.Beamforming may be achieved by combining the signals communicated viaantenna elements of an antenna array such that signals propagating atparticular orientations with respect to an antenna array experienceconstructive interference while others experience destructiveinterference. The adjustment of signals communicated via the antennaelements may include a transmitting device or a receiving deviceapplying certain amplitude and phase offsets to signals carried via eachof the antenna elements associated with the device. The adjustmentsassociated with each of the antenna elements may be defined by abeamforming weight set associated with a particular orientation (e.g.,with respect to the antenna array of the transmitting device orreceiving device, or with respect to some other orientation).

In one example, a base station 105 may use multiple antennas or antennaarrays to conduct beamforming operations for directional communicationswith a UE 115. For instance, some signals (e.g. synchronization signals,reference signals, beam selection signals, or other control signals) maybe transmitted by a base station 105 multiple times in differentdirections, which may include a signal being transmitted according todifferent beamforming weight sets associated with different directionsof transmission. Transmissions in different beam directions may be usedto identify (e.g., by the base station 105 or a receiving device, suchas a UE 115) a beam direction for subsequent transmission and/orreception by the base station 105. Some signals, such as data signalsassociated with a particular receiving device, may be transmitted by abase station 105 in a single beam direction (e.g., a directionassociated with the receiving device, such as a UE 115). In someexamples, the beam direction associated with transmissions along asingle beam direction may be determined based at least in in part on asignal that was transmitted in different beam directions. For example, aUE 115 may receive one or more of the signals transmitted by the basestation 105 in different directions, and the UE 115 may report to thebase station 105 an indication of the signal it received with a highestsignal quality, or an otherwise acceptable signal quality. Althoughthese techniques are described with reference to signals transmitted inone or more directions by a base station 105, a UE 115 may employsimilar techniques for transmitting signals multiple times in differentdirections (e.g., for identifying a beam direction for subsequenttransmission or reception by the UE 115), or transmitting a signal in asingle direction (e.g., for transmitting data to a receiving device).

A receiving device (e.g., a UE 115, which may be an example of a mmWreceiving device) may try multiple receive beams when receiving varioussignals from the base station 105, such as synchronization signals,reference signals, beam selection signals, or other control signals. Forexample, a receiving device may try multiple receive directions byreceiving via different antenna subarrays, by processing receivedsignals according to different antenna subarrays, by receiving accordingto different receive beamforming weight sets applied to signals receivedat a plurality of antenna elements of an antenna array, or by processingreceived signals according to different receive beamforming weight setsapplied to signals received at a plurality of antenna elements of anantenna array, any of which may be referred to as “listening” accordingto different receive beams or receive directions. In some examples areceiving device may use a single receive beam to receive along a singlebeam direction (e.g., when receiving a data signal). The single receivebeam may be aligned in a beam direction determined based at least inpart on listening according to different receive beam directions (e.g.,a beam direction determined to have a highest signal strength, highestsignal-to-noise ratio, or otherwise acceptable signal quality based atleast in part on listening according to multiple beam directions).

In some cases, the antennas of a base station 105 or UE 115 may belocated within one or more antenna arrays, which may support MIMOoperations, or transmit or receive beamforming. For example, one or morebase station antennas or antenna arrays may be co-located at an antennaassembly, such as an antenna tower. In some cases, antennas or antennaarrays associated with a base station 105 may be located in diversegeographic locations. A base station 105 may have an antenna array witha number of rows and columns of antenna ports that the base station 105may use to support beamforming of communications with a UE 115.Likewise, a UE 115 may have one or more antenna arrays that may supportvarious MIMO or beamforming operations.

In some cases, wireless communications system 100 may be a packet-basednetwork that operate according to a layered protocol stack. In the userplane, communications at the bearer or Packet Data Convergence Protocol(PDCP) layer may be IP-based. A Radio Link Control (RLC) layer may insome cases perform packet segmentation and reassembly to communicateover logical channels. A Medium Access Control (MAC) layer may performpriority handling and multiplexing of logical channels into transportchannels. The MAC layer may also use hybrid automatic repeat request(HARQ) to provide retransmission at the MAC layer to improve linkefficiency. In the control plane, the Radio Resource Control (RRC)protocol layer may provide establishment, configuration, and maintenanceof an RRC connection between a UE 115 and a base station 105 or corenetwork 130 supporting radio bearers for user plane data. At thePhysical (PHY) layer, transport channels may be mapped to physicalchannels.

In some cases, UEs 115 and base stations 105 may support retransmissionsof data to increase the likelihood that data is received successfully.HARQ feedback is one technique of increasing the likelihood that data isreceived correctly over a communication link 125. HARQ may include acombination of error detection (e.g., using a cyclic redundancy check(CRC)), forward error correction (FEC), and retransmission (e.g.,automatic repeat request (ARQ)). HARQ may improve throughput at the MAClayer in poor radio conditions (e.g., signal-to-noise conditions). Insome cases, a wireless device may support same-slot HARQ feedback, wherethe device may provide HARQ feedback in a specific slot for datareceived in a previous symbol in the slot. In other cases, the devicemay provide HARQ feedback in a subsequent slot, or according to someother time interval.

Time intervals in LTE or NR may be expressed in multiples of a basictime unit, which may, for example, refer to a sampling period ofT_(s)=1/30,720,000 seconds. Time intervals of a communications resourcemay be organized according to radio frames each having a duration of 10milliseconds (ms), where the frame period may be expressed as Tf=307,200T_(s). The radio frames may be identified by a system frame number (SFN)ranging from 0 to 1023. Each frame may include 10 subframes numberedfrom 0 to 9, and each subframe may have a duration of 1 ms. A subframemay be further divided into 2 slots each having a duration of 0.5 ms,and each slot may contain 6 or 7 modulation symbol periods (e.g.,depending on the length of the cyclic prefix prepended to each symbolperiod). Excluding the cyclic prefix, each symbol period may contain2048 sampling periods. In some cases a subframe may be the smallestscheduling unit of the wireless communications system 100, and may bereferred to as a transmission time interval (TTI). In other cases, asmallest scheduling unit of the wireless communications system 100 maybe shorter than a subframe or may be dynamically selected (e.g., inbursts of shortened TTIs (sTTIs) or in selected component carriers usingsTTIs).

In some wireless communications systems, a slot may further be dividedinto multiple mini-slots containing one or more symbols. In someinstances, a symbol of a mini-slot or a mini-slot may be the smallestunit of scheduling. Each symbol may vary in duration depending on thesubcarrier spacing or frequency band of operation, for example. Further,some wireless communications systems may implement slot aggregation inwhich multiple slots or mini-slots are aggregated together and used forcommunication between a UE 115 and a base station 105.

The term “carrier” refers to a set of radio frequency spectrum resourceshaving a defined physical layer structure for supporting communicationsover a communication link 125. For example, a carrier of a communicationlink 125 may include a portion of a radio frequency spectrum band thatis operated according to physical layer channels for a given radioaccess technology. Each physical layer channel may carry user data,control information, or other signaling. A carrier may be associatedwith a pre-defined frequency channel (e.g., an E-UTRA absolute radiofrequency channel number (EARFCN)), and may be positioned according to achannel raster for discovery by UEs 115. Carriers may be downlink oruplink (e.g., in an FDD mode), or be configured to carry downlink anduplink communications (e.g., in a TDD mode). In some examples, signalwaveforms transmitted over a carrier may be made up of multiplesub-carriers (e.g., using multi-carrier modulation (MCM) techniques suchas OFDM or DFT-s-OFDM).

The organizational structure of the carriers may be different fordifferent radio access technologies (e.g., LTE, LTE-A, LTE-A Pro, NR,etc.). For example, communications over a carrier may be organizedaccording to TTIs or slots, each of which may include user data as wellas control information or signaling to support decoding the user data. Acarrier may also include dedicated acquisition signaling (e.g.,synchronization signals or system information, etc.) and controlsignaling that coordinates operation for the carrier. In some examples(e.g., in a carrier aggregation configuration), a carrier may also haveacquisition signaling or control signaling that coordinates operationsfor other carriers.

Physical channels may be multiplexed on a carrier according to varioustechniques. A physical control channel and a physical data channel maybe multiplexed on a downlink carrier, for example, using time divisionmultiplexing (TDM) techniques, frequency division multiplexing (FDM)techniques, or hybrid TDM-FDM techniques. In some examples, controlinformation transmitted in a physical control channel may be distributedbetween different control regions in a cascaded manner (e.g., between acommon control region or common search space and one or more UE-specificcontrol regions or UE-specific search spaces).

A carrier may be associated with a particular bandwidth of the radiofrequency spectrum, and in some examples the carrier bandwidth may bereferred to as a “system bandwidth” of the carrier or the wirelesscommunications system 100. For example, the carrier bandwidth may be oneof a number of predetermined bandwidths for carriers of a particularradio access technology (e.g., 1.4, 3, 5, 10, 15, 20, 40, or 80 MHz). Insome examples, each served UE 115 may be configured for operating overportions or all of the carrier bandwidth. In other examples, some UEs115 may be configured for operation using a narrowband protocol typethat is associated with a predefined portion or range (e.g., set ofsubcarriers or RBs) within a carrier (e.g., “in-band” deployment of anarrowband protocol type).

In a system employing MCM techniques, a resource element may consist ofone symbol period (e.g., a duration of one modulation symbol) and onesubcarrier, where the symbol period and subcarrier spacing are inverselyrelated. The number of bits carried by each resource element may dependon the modulation scheme (e.g., the order of the modulation scheme).Thus, the more resource elements that a UE 115 receives and the higherthe order of the modulation scheme, the higher the data rate may be forthe UE 115. In MIMO systems, a wireless communications resource mayrefer to a combination of a radio frequency spectrum resource, a timeresource, and a spatial resource (e.g., spatial layers), and the use ofmultiple spatial layers may further increase the data rate forcommunications with a UE 115.

Devices of the wireless communications system 100 (e.g., base stations105 or UEs 115) may have a hardware configuration that supportscommunications over a particular carrier bandwidth, or may beconfigurable to support communications over one of a set of carrierbandwidths. In some examples, the wireless communications system 100 mayinclude base stations 105 and/or UEs that can support simultaneouscommunications via carriers associated with more than one differentcarrier bandwidth.

Wireless communications system 100 may support communication with a UE115 on multiple cells or carriers, a feature which may be referred to ascarrier aggregation (CA) or multi-carrier operation. A UE 115 may beconfigured with multiple downlink CCs and one or more uplink CCsaccording to a carrier aggregation configuration. Carrier aggregationmay be used with both FDD and TDD component carriers.

In some cases, wireless communications system 100 may utilize enhancedcomponent carriers (eCCs). An eCC may be characterized by one or morefeatures including wider carrier or frequency channel bandwidth, shortersymbol duration, shorter TTI duration, or modified control channelconfiguration. In some cases, an eCC may be associated with a carrieraggregation configuration or a dual connectivity configuration (e.g.,when multiple serving cells have a suboptimal or non-ideal backhaullink). An eCC may also be configured for use in unlicensed spectrum orshared spectrum (e.g., where more than one operator is allowed to usethe spectrum). An eCC characterized by wide carrier bandwidth mayinclude one or more segments that may be utilized by UEs 115 that arenot capable of monitoring the whole carrier bandwidth or are otherwiseconfigured to use a limited carrier bandwidth (e.g., to conserve power).

In some cases, an eCC may utilize a different symbol duration than otherCCs, which may include use of a reduced symbol duration as compared withsymbol durations of the other CCs. A shorter symbol duration may beassociated with increased spacing between adjacent subcarriers. Adevice, such as a UE 115 or base station 105, utilizing eCCs maytransmit wideband signals (e.g., according to frequency channel orcarrier bandwidths of 20, 40, 60, 80 MHz, etc.) at reduced symboldurations (e.g., 16.67 microseconds). A TTI in eCC may consist of one ormultiple symbol periods. In some cases, the TTI duration (that is, thenumber of symbol periods in a TTI) may be variable.

Wireless communications systems such as an NR system may utilize anycombination of licensed, shared, and unlicensed spectrum bands, amongothers. The flexibility of eCC symbol duration and subcarrier spacingmay allow for the use of eCC across multiple spectrums. In someexamples, NR shared spectrum may increase spectrum utilization andspectral efficiency, specifically through dynamic vertical (e.g., acrossfrequency) and horizontal (e.g., across time) sharing of resources.

A base station 105 or UE 115 may modulate a digital signal by modifyingone or more properties of a periodic waveform (e.g., frequency,amplitude, phase, etc.) prior to transmitting to a receiving device. Forexample, a BPSK modulation scheme may convey information by alternatingbetween waveforms that are transmitted with no phase offset or with a180° offset, and each symbol may convey a single bit of information.

In a QAM modulation scheme, two waveforms (known as the in-phasecomponent (I) and the quadrature component (Q)) may be transmitted witha phase offset of 90°, and during a symbol duration, each the I and Qcomponents may each be transmitted with a specific amplitude selectedfrom a finite set. The amplitude combinations of the I and Q componentsmay be represented in a graph known as a constellation map, where theamplitude of the I component is represented on the horizontal axis, theQ component is represented on the vertical axis, and each point in theconstellation corresponds to a valid QAM symbol.

Each valid QAM symbol may also be considered as a combination of the Iand Q components, with each point in the constellation corresponding toa valid phase and amplitude combination for the combined signal. Thenumber of valid phase and amplitude combinations may determine thenumber of bits that are conveyed by each QAM symbol. For example, a16QAM modulation scheme may define sixteen (16) valid phase andamplitude combinations, and thus each 16QAM symbol may represent four(4) bits, as 2⁴ is 16. Similarly, a 64QAM modulation scheme may definesixteen (64) valid phase and amplitude combinations, and thus each 64QAMsymbol may represent six (6) bits, as 2⁶ is 64. The more number of bitsrepresented by a single symbol, the higher the order of the modulationscheme or symbol. Wireless communications system 100 may in some casesuse QAM modulation schemes higher in order than 16QAM or 64QAM, such as256QAM and 1024QAM. As the order of a QAM modulation scheme increases,valid phase and amplitude combinations may be separated by finer (thatis, smaller) phase differences, and thus the detrimental impact of phaseerrors may increase.

Base stations 105 and UEs 115 may support the techniques describedherein for identifying and correcting phase errors at a receivingdevice, including on a sub-symbol level time scale, which may improvethe ability of base stations 105 and UEs 115 to use higher-ordermodulation techniques. Thus, by improving the ability of base stations105 and UEs 115 to represent more information (that is, a greater numberof bits) with each symbol, the systems and techniques described hereinmay improve the efficiency with which a wireless communications system100 utilizes spectrum, power, frequency, time, code, and otherresources.

FIG. 2 illustrates an example of a wireless communications system 200that supports a PT-RS for sub-symbol phase tracking in accordance withvarious aspects of the present disclosure. In some examples, wirelesscommunications system 200 may include aspects of wireless communicationssystem 100. For example, wireless communications system includes a basestation 105-a and a UE 115-a, which may be examples of a base station105 and a UE 115 as described with reference to FIG. 1.

The base station 105-a may transmit to the UE 115-a a wireless signal205 that includes a number of subcarriers, each subcarrier having adifferent frequency. The base station 105-a may frequency multiplexsymbols by mapping the symbols to different subcarriers with thewireless signal 205. Each of the subcarriers may be modulated usingvarious modulation schemes such as QAM, PSK, etc. However, phase errorsmay arise due to a variety of factors. These factors may include phasenoise, carrier frequency offset, Doppler effect. The impact of phaseerrors may increase as the order of modulation increases, which mayimpact the performance of a wireless system. Techniques to addressidentifying and correcting phase errors at wireless devices aredescribed herein.

In some cases, the base station 105-a and the UE 115-a may perform DFTsand inverse DFTs (IDFTs). A DFT may transform discrete time data setsinto a discrete frequency representation, and an IDFT may transform adiscrete frequency representation (e.g., information represented indiscrete frequencies) into a discrete time representation (e.g., adigital signal carrying information in the time domain). In some cases,the base station 105-a may precode some symbols according to a DFT, thenfrequency division multiplex the DFT-precoded symbols with other symbols(e.g., non-DFT-precoded symbols) by mapping the DFT-precoded symbols andthe other symbols to different subcarriers within the wireless signal205. The other symbols may comprise data, control information, orreference information and thus may be referred to as data, control, orreference symbols.

The base station 105-a may map at least some of the DFT-precoded symbolsto adjacent subcarriers (that is, adjacent frequency tones) within thewireless signal 205. Further, the base station 105 may use one or moresize-M DFT modules (which may also be referred to as M-point DFTmodules) to generate the DFT-precoded symbols. For example, the basestation 105-a may use a single size-M DFT module to generate MDFT-precoded symbols, and may map the M DFT-precoded symbols to a singleset of M adjacent subcarriers within the wireless signal 205 whilemapping other symbols to other subcarriers within the wireless signal205. As another example, the base station 105-a may use multiple size-MDFT modules to generate multiple sets of M DFT-precoded symbols, and maymap each set of M DFT-precoded symbols to a respective set of M adjacentsubcarriers, while mapping other symbols to other subcarriers within thewireless signal 205. The other subcarriers may in some cases beinterposed between sets of M adjacent subcarriers. Thus, the number ofDFT modules used by the base station 105-a to generate DFT-precodedsymbols may vary, as may the size of each DFT module. In some cases, theDFT-precoded symbols may be PT-RS symbols. For example, the DFT-precodedsymbols may be PT-RS symbols that each correspond to a distinct PT-RSsequence.

The UE 115 may receive the wireless signal and may estimate a phaseerror based at least in part on the DFT-precoded symbols. In some cases,the UE 115 may estimate the phase error with sub-symbol resolution basedat least in part on the DFT-precoded symbols carried by adjacentsubcarriers. The UE 115 may then apply a phase error correction to theother symbols based at least in part on the estimated phase error. Insome cases, the UE 115 may estimate the phase error, at least in part,by performing an IDFT of the DFT-precoded symbols to obtain a timedomain representation of the DFT-precoded symbols and comparing the timedomain representation of the DFT-precoded symbols with a time domainrepresentation of a corresponding set of reference symbols (e.g.,symbols of reference PT-RS sequences).

The resolution in the time domain with which the UE 115 may estimate thephase error may relate to the size ‘M’ of the one or more DFT modulesused by base station 105 to precode the DFT-precoded symbols. Forexample, the UE 115 may estimate the phase error with a resolution of ¼of a symbol in the time domain if the base station 105 uses one or moresize-4 DFT modules (which may also be referred to as 4-point DFTmodules), the UE 115 may estimate the phase error with a resolution of ⅛of a symbol in the time domain if the base station 105 uses one or moresize-8 DFT modules (which may also be referred to as 8-point DFTmodules), and so on.

FIG. 3 illustrates an example of a DFT-precoding system 300 thatsupports a PT-RS for sub-symbol phase tracking in accordance withvarious aspects of the present disclosure. In some examples,DFT-precoding system 300 may be included in aspects of wirelesscommunications system 100 or wireless communications system 200. Forexample, DFT-precoding system 300 may be included in a base station 105.DFT-precoding system 300 may include one or more size-M DFT modules 305,a mapper 310, and a size-N IDFT module 315.

The base station 105 may determine a DFT configuration for DFT-precodingsystem 300, which may include determining the number and size of DFTmodules 305. As illustrated in the example of FIG. 3, DFT-precodingsystem 300 includes three DFT modules 305, each size-4 as indicated bythe four inputs and outputs of each DFT module 305 illustrated in FIG.3, but the base station 105 may determine any number of DFT modules 305of any size (e.g., any value of M) in other examples.

Each size-M DFT module 305 may receive M time domain symbols 320 and maygenerate and output M DFT-precoded symbols 325. The symbols 320 may insome cases be reference signal symbols, such as PT-RS symbols. Forexample, the M symbols 320 may respectively correspond to M distincttime domain PT-RS sequences, and thus each of the M symbols 320 maycorrespond to a distinct time domain PT-RS sequence. Each symbol 320,prior to any DFT-precoding, may be equal in magnitude to one another,and thus power for the purpose of phase tracking by a receiving device(e.g., a UE 115) may be equally distributed in the time domain across anindividual symbol.

In some cases, the DFT modules 305 may generate DFT-precoded symbols 325without executing DFT operations at the time of a transmission. Forexample, DFT-precoded symbols 325 may be generated for possible symbols320 in advance and stored in memory within the base station 105. At thetime of a given transmission, a DFT module 305 may generate DFT-precodedsymbols 325 by retrieving from memory a plurality of DFT-precodedsymbols 325 that have been computed in advance and associated with thesymbols 320 and the operative DFT configuration. For example, the DFTmodules 305 may access (or consult) a lookup table that associatespre-computed DFT-precoded symbols 325 with the symbols 320 and theoperative DFT configuration.

In some cases, the base station 105 may determine the DFT configurationfor DFT-precoding system 300 based at least in part on the total numberof symbols 320. For example, if the total number of symbols is ‘X,’ andthe total number of DFT modules is ‘Y,’ the base station 105 maydetermine Y and M such that Y multiplied by M equals X (that is, Y*M=X).The base station 105 may also determine Y and M based at least in parton a desired resolution for phase tracking and phase error estimationand also on noise and fading considerations. For example, a larger valueof M may correspond to enhanced resolution for phase tracking and phaseerror estimation (e.g., M=4 may support phase tracking and phase errorestimation in the time domain with a resolution of ¼ of a symbol period,M=8 may support phase tracking and phase error estimation in the timedomain with a resolution of ⅛ of a symbol period, and so on). On theother hand, a smaller value of M—and thus a larger value of Y—maycorrespond to enhanced robustness to noise and frequency selectivefading in a communications channel due to frequency diversity effects,as the use of more DFT modules 305 may allow at least some DFT-precodedsymbols 325 to be separated from one another in frequency.

Accordingly, in some cases the DFT configuration may be variable, andthe base station 105 may determine the DFT configuration based at leastin part on factors related to characteristics of the subcarriers 335 towhich the mapper 310 may map the DFT-precoded symbols 325. For example,the base station 105 may determine the DFT configuration based at leastin part on one or more of a modulation and coding scheme (MCS), asignal-to-noise ratio (SNR), a phase noise, or a CFO associated with atleast one of the subcarriers 335 to which the mapper 310 may map theDFT-precoded symbols 325. In some cases, the base station 105 maytransmit to a target wireless device (e.g., a target UE 115) anindication of the DFT configuration used to generate a given set ofDFT-precoded symbols 325. In some cases, the base station 105 mayreceive from a target wireless device (e.g., a target UE 115) anindication of a preferred DFT configuration, and the base station 105may use the preferred DFT configuration to generate a given set ofDFT-precoded symbols 325.

Mapper 310 may receive one or more sets of DFT-precoded symbols 325,each set of DFT-precoded symbols 325 corresponding to a distinct DFTmodule 305, and may map the sets of DFT-precoded symbols 325 tocorresponding sets of adjacent subcarriers 335. The adjacent subcarriers335 included in the corresponding sets of adjacent subcarriers 335 maybe adjacent in frequency (e.g., may comprise adjacent tones). Thus, themapper 310 may map any DFT-precoded symbols 325 generated by a given DFTmodule 305 to respective subcarriers 335 that are adjacent in frequency.Mapping M DFT-precoded symbols 325 to adjacent subcarriers 335 maybeneficially support phase tracking and phase error estimation in thetime domain with a resolution of 1/M of a symbol period, which may, forexample, support the use of higher-order modulation techniques.

Mapper 310 may also receive one or more additional symbols 330, whichmay be in the frequency domain but not DFT-precoded (e.g., not processedby any DFT module 305). The additional symbols may be of any symbol typeand may, for example, be data symbols, control symbols, or referencesignal symbols representing data information, control information, orreference signal information. Mapper 310 may frequency divisionmultiplex the additional symbols 330 with the DFT-precoded symbols 325.Thus, DFT-precoding system 300 may frequency division multiplexDFT-precoded symbols 325 with other symbols (data symbols, controlsymbols, or reference symbols) that are not DFT-precoded.

For example, if the DFT configuration comprises multiple DFT modules305, as in the example of DFT-precoding system 300, mapper 310 may mapat least one additional symbol 330 to a subcarrier 335 that is betweentwo sets of adjacent subcarriers 335 to which the mapper 310 mapsDFT-precoded symbols 325, as illustrated in FIG. 3. As another example,if the DFT configuration comprises only one DFT module 305, mapper 310may map at least one additional symbol 330 to a subcarrier 335 that isadjacent in frequency to a subcarrier 335 to which the mapper 310 mapsDFT-precoded symbols 325 (e.g., adjacent in frequency to one subcarrier335 of a set of adjacent subcarriers 335 to which the mapper 310 mapsDFT-precoded symbols 325). Mapper 310 may seek to distribute sets ofadjacent subcarriers 335 to which mapper 310 maps DFT-precoded symbols325 so as to support phase tracking and phase error estimation acrossthe total bandwidth spanned by the subcarriers 335 and to enhance thefrequency diversity of different sets of adjacent subcarriers 335relative to one another.

In some cases, the mapper 310 may determine the subcarriers 335 to whichthe mapper 310 maps DFT-precoded symbols 325 based at least in part onchannel quality considerations. For example, the mapper 310 may mapDFT-precoded symbols 325 to subcarriers 335 having better channelquality (e.g., lower SNR) relative to other subcarriers 335, as this mayenhance the ability of a target receiving device (e.g., a target UE 115)to perform phase tracking and phase error corrections. In some cases,the base station 105 may receive channel quality information (e.g.,channel measurement reports) from another wireless device (e.g., thetarget receiving device or some other wireless device, such as anotherbase station 105 or UE 115), and the mapper 310 may determine one ormore of the subcarriers 335 to which the mapper 310 maps DFT-precodedsymbols 325 based at least in part on the channel quality informationreceived from the base station 105. Additionally or alternatively, thebase station 105 may receive from another wireless device one or moresignals (e.g., reference signals) based upon which the base station 105may determine channel quality information, and the mapper 310 maydetermine one or more of the subcarriers 335 to which the mapper 310maps DFT-precoded symbols 325 based at least in part on the channelquality information determined by the base station 105. Channel qualityinformation received or determined by the base station 105 may includeSNR information for one or more of the subcarriers 335.

Additionally or alternatively, the base station 105 may in some casesreceive an indication of one or more preferred subcarriers 335 fromanother wireless device, and the mapper 310 may map one or moreDFT-precoded symbols 325 to the one or more preferred subcarriers 335.Also, the base station 105 may transmit to a target wireless device(e.g., a target UE 115) an indication of the subcarriers 335 to whichmapper 310 maps DFT-precoded symbols 325.

The mapper 310 may output the subcarriers 335 to which the mappers havemapped DFT-precoded symbols 325 and additional symbols 330 to the size-NIDFT module 315. N may be the number of subcarriers 335, and the size-NIDFT module may execute IDFT operations to transform the informationmapped to the N subcarriers 335 into N corresponding discrete timedomain representations 340 (e.g., digital signals carrying informationin the time domain). Afterwards, the base station 105 may performadditional processing on the time domain representations 340 (e.g.,serializing, such as parallel-to-serial conversion, prepending of acyclic prefix to each time domain symbol, etc.) and may transmit awireless signal that includes the subcarriers 335.

Although the operation of DFT-precoding system 300 has been described inthe context of a single symbol duration, it is to be understood that theexample of DFT-precoding system 300 and other examples in accordancewith various aspects of the present disclosure may repeat duringmultiple consecutive or non-consecutive symbol durations.

FIG. 4 illustrates an example of a phase error compensation system 400that supports a PT-RS for sub-symbol phase tracking in accordance withvarious aspects of the present disclosure. In some examples, phase errorcompensation system 400 may be included in aspects of wirelesscommunications system 100 or wireless communications system 200. Forexample, phase error compensation system 400 may be included in a UE115. Phase error compensation system 400 may include a size-N DFT module405, one or more size-M IDFT modules 410, a phase error estimator 415,and a phase error corrector 420.

The UE 115 may receive a wireless signal that includes a plurality ofsubcarriers 335 from a transmitting device (e.g., a base station 105).The wireless signal may have been processed by a DFT-precoding system300 such as the example described in reference to FIG. 3. Thus, some ofthe received subcarriers 335 may carry DFT-precoded symbols 325 and someof the received subcarriers 335 may carry additional symbols 330 (e.g.symbols that were not DFT-precoded prior to transmission), andDFT-precoded symbols 325 may be multiplexed with additional symbols 330.Further, sets of DFT-precoded symbols generated by individual DFTmodules 305 may be received via correspond sets of adjacent subcarriers335.

The UE 115 may identify a DFT configuration for the DFT-precodedsymbols. For example, the UE 115 may identify a number of DFT modules305 used by the transmitting device to precode the DFT-precoded symbolsand a size of each DFT module 305 used to precode the DFT-precodedsymbols. In some cases, the UE 115 may receive from the transmittingdevice an indication of the DFT configuration. In some cases, the UE 115or another wireless node (e.g., another UE 115 or a base station 105)may transmit to the transmitting device an indication of a preferred DFTconfiguration, and the transmitting device may be configured to use thepreferred DFT configuration or to notify the UE 115 if it does or doesnot use the preferred DFT configuration.

The UE 115 may also identify the subcarriers 335 that carry theDFT-precoded symbols 325. In some cases, the UE 115 may receive from thetransmitting device an indication of the subcarriers 335 that carry theDFT-precoded symbols 325. In some cases, the UE 115 or another wirelessnode may transmit to the transmitting device an indication of one ormore preferred subcarriers 335 for DFT-precoded symbols 325, and thetransmitting device may be configured to map the DFT-precoded symbols325 to the preferred subcarriers 335 or to notify the UE 115 if it doesor does not map the DFT-precoded symbols 325 to the preferredsubcarriers 335. In some cases, the UE 115 may determine the preferredsubcarriers 335 based at least in part on one or more associated channelquality metrics, such as SNR.

The UE 115 may perform some preliminary processing on the wirelesssignal (e.g., removal of cyclic prefixes, serial-to-parallel conversion,etc.), then process the DFT-precoded symbols 325 based at least in parton the identified DFT configuration to obtain a corresponding pluralityof symbols. For example, the UE 115 may pass a plurality of time domainrepresentations 425 of the received DFT-precoded symbols 325 and thereceived additional symbols 330 to the size-N DFT module, where N may bethe number of received subcarriers 335. The size-N DFT module maygenerate N frequency domain representations corresponding to the N timedomain representations 425. For example, the size-N DFT module maygenerate M frequency domain representations 430 of each set of MDFT-precoded symbols 325 corresponding to a DFT module 305 and may alsogenerate a frequency domain representation 440 of each additional symbol330.

The size-N DFT module may pass the M frequency domain representations430 of each set of M DFT-precoded symbols 325 to a corresponding size-MIDFT module 410. The UE 115 may configure the number and size of theIDFT modules 410 based on the identified DFT configuration for theDFT-precoded symbols 325 (e.g., the UE 115 may configure the number andsize of the IDFT modules 410 to match the number and size of the DFTmodules 305 used to generate the DFT-precoded symbols 325). Each size-MIDFT module 410 may generate a set of M time domain symbols 435corresponding to each set of M DFT-precoded symbols 325 based on an IDFTalgorithm and may pass the time domain symbols 435 to the phase errorestimator 415.

In some cases, the IDFT modules 410 may not execute IDFT operations atthe time DFT-precoded symbols 325 are received. For example, time domainsymbols 435 corresponding to the possible DFT-precoded symbols 325 maybe generated in advance and stored in memory within the UE 115. At thetime of a given transmission, an IDFT module 410 may generate the timedomain symbols 435 by retrieving from memory a plurality of time domainsymbols 435 that have been computed in advance and associated with theDFT-precoded symbols 325 and the operative DFT configuration. Forexample, the IDFT modules 410 may access (or consult) a lookup tablethat associates pre-computed time domain symbols 435 with DFT-precodedsymbols 325 and the operative DFT configuration.

The phase error estimator 415 may receive X time domain symbols 435(where X is the total number of DFT-precoded symbols 325, as describedin reference to FIG. 3) and may estimate one or more phase errors basedat least in part on the X time domain symbols 435. For example, thephase error estimator may retrieve from memory X reference symbols 445and compare the X time domain symbols 435 to the X reference symbols 445in the time domain. In some cases, the UE 115 may receive an indicationfrom the transmitting device of the symbols 320 for which theDFT-precoded symbols 325 were generated and may retrieve from memoryreference symbols 445 that correspond to the symbols 320 for which theDFT-precoded symbols 325 were generated. Alternatively or additionally,the UE 115 may receive an indication from the transmitting device of thereference symbols 445 to use for phase error estimation. In some cases,the plurality of DFT-precoded symbols 325 may correspond to a pluralityof PT-RS symbols, and thus the time domain symbols 435 may be timedomain versions of the received PT-RS symbols and the reference symbols445 may be reference PT-RS symbols. In some cases, each reference PT-RSsymbol may be part of a distinct PT-RS sequence, and the indication ofthe reference symbols 445 may indicate the corresponding PT-RSsequences.

By comparing the X time domain symbols 435 to the X reference symbols445 in the time domain, where M DFT-precoded symbols 325 were receivedvia adjacent subcarriers 335, the phase error estimator 415 may supportphase tracking and phase error estimation in the time domain with aresolution of 1/M of a symbol period, which may, for example, supportthe use of higher-order modulation techniques.

Further, generating the DFT-precoded symbols 325, by the transmittingdevice, using a DFT-configuration and symbols 320 that are known to theUE 115 may further support phase tracing and phase error estimation bythe UE. For example, because the UE 115 may know exactly which symbols320 were DFT-precoded and the exact DFT configuration used to generatethe corresponding DFT-precoded symbols, the UE 115 may be able todetermine a corresponding configuration of IDFT modules 410 and acorresponding set of reference symbols 445, and thus may support thevalidity of the comparison of time domain symbols 435 to referencesymbols 445 by the phase error estimator 415. Further, DFT-precoding ofthe DFT-precoded symbols 325 may ensure that power in the time domain isequally distributed within each of time domain symbols 435, thus furthersupporting the validity of the comparison of time domain symbols 435 toreference symbols 445 by the phase error estimator 415.

The phase error estimator 415 may in some cases compute a phase errortrajectory based on the comparison of time domain symbols 435 toreference symbols 445. The phase error trajectory may comprise atrajectory of phase error across the bandwidth of the wireless signal(e.g., across the frequencies corresponding to the received subcarriers335), as a phase error may be computed for multiple subcarriers viawhich DFT-precoded symbols 325 were received, and a phase error for oneor more other subcarriers 335 at other frequencies may be extrapolatedor interpolated therefrom, as applicable

The phase error corrector 420 may apply a phase correction (e.g., aphase adjustment) to the frequency domain representation 440 of one ormore of the additional symbols 330 based at least in part on the phaseerror computed by the phase error estimator. In some cases, the phaseerror corrector 420 may receive from the phase error estimator 415 aseparate phase error estimate 450 corresponding to each additionalsymbol 330 (e.g., phase error corrector 420 may receive N-X phase errorestimates 450 from the phase error estimator 415), and the phase errorcorrector 420 may apply a corresponding phase correction to thefrequency domain representation 440 of each of the additional symbols330, resulting in a phase-corrected representation 455 of each of theadditional symbols 330. Further, although in the example of phase errorcompensation system 400 the phase error corrector 420 is shown asapplying phase corrections in the frequency domain, in other examples,the phase error corrector 420 may apply phase corrections in the timedomain. For example, the phase error corrector may apply phasecorrections to time domain representations of the additional symbols330.

Although the operation of phase error compensation system 400 has beendescribed in the context of a single symbol duration, it is to beunderstood that the example of phase error compensation system 400 andother examples in accordance with various aspects of the presentdisclosure may repeat for during multiple consecutive or non-consecutivesymbol durations.

FIG. 5 shows a block diagram 500 of a wireless device 505 that supportsa PT-RS for sub-symbol phase tracking in accordance with aspects of thepresent disclosure. Wireless device 505 may be an example of aspects ofa base station 105 as described herein. Wireless device 505 may includereceiver 510, base station communications manager 515, and transmitter520. Wireless device 505 may also include a processor. Each of thesecomponents may be in communication with one another (e.g., via one ormore buses).

Receiver 510 may receive information such as packets, user data, orcontrol information associated with various information channels (e.g.,control channels, data channels, and information related to phasetracking reference signal for sub-symbol phase tracking, etc.).Information may be passed on to other components of the device. Thereceiver 510 may be an example of aspects of the transceiver 835described with reference to FIG. 8. The receiver 510 may utilize asingle antenna or a set of antennas.

Base station communications manager 515 may be an example of aspects ofthe base station communications manager 815 described with reference toFIG. 8.

Base station communications manager 515 and/or at least some of itsvarious sub-components may be implemented in hardware, software executedby a processor, firmware, or any combination thereof. If implemented insoftware executed by a processor, the functions of the base stationcommunications manager 515 and/or at least some of its varioussub-components may be executed by a general-purpose processor, a digitalsignal processor (DSP), an application-specific integrated circuit(ASIC), an field-programmable gate array (FPGA) or other programmablelogic device, discrete gate or transistor logic, discrete hardwarecomponents, or any combination thereof designed to perform the functionsdescribed in the present disclosure. The base station communicationsmanager 515 and/or at least some of its various sub-components may bephysically located at various positions, including being distributedsuch that portions of functions are implemented at different physicallocations by one or more physical devices. In some examples, basestation communications manager 515 and/or at least some of its varioussub-components may be a separate and distinct component in accordancewith various aspects of the present disclosure. In other examples, basestation communications manager 515 and/or at least some of its varioussub-components may be combined with one or more other hardwarecomponents, including but not limited to an I/O component, atransceiver, a network server, another computing device, one or moreother components described in the present disclosure, or a combinationthereof in accordance with various aspects of the present disclosure.

Base station communications manager 515 may determine a DFTconfiguration for a set of symbols, generate, based on the DFTconfiguration, a set of DFT-precoded symbols corresponding to the set ofsymbols, map the set of DFT-precoded symbols to a corresponding set ofsubcarriers, the set of subcarriers including at least a subset ofsubcarriers that are adjacent in frequency, map additional symbols toadditional subcarriers, and transmit the set of DFT-precoded symbols viaa wireless signal that includes the set of subcarriers and theadditional subcarriers.

Transmitter 520 may transmit signals generated by other components ofthe device. In some examples, the transmitter 520 may be collocated witha receiver 510 in a transceiver module. For example, the transmitter 520may be an example of aspects of the transceiver 835 described withreference to FIG. 8. The transmitter 520 may utilize a single antenna ora set of antennas.

FIG. 6 shows a block diagram 600 of a wireless device 605 that supportsa PT-RS for sub-symbol phase tracking in accordance with aspects of thepresent disclosure. Wireless device 605 may be an example of aspects ofa wireless device 505 or a base station 105 as described with referenceto FIG. 5. Wireless device 605 may include receiver 610, base stationcommunications manager 615, and transmitter 620. Wireless device 605 mayalso include a processor. Each of these components may be incommunication with one another (e.g., via one or more buses).

Receiver 610 may receive information such as packets, user data, orcontrol information associated with various information channels (e.g.,control channels, data channels, and information related to phasetracking reference signal for sub-symbol phase tracking, etc.).Information may be passed on to other components of the device. Thereceiver 610 may be an example of aspects of the transceiver 835described with reference to FIG. 8. The receiver 610 may utilize asingle antenna or a set of antennas.

Base station communications manager 615 may be an example of aspects ofthe base station communications manager 815 described with reference toFIG. 8. Base station communications manager 615 may also include DFTconfiguration component 625, DFT component 630, mapping component 635,and transmission component 640.

DFT configuration component 625 may determine a DFT configuration for aset of symbols. In some cases, determining the DFT configurationincludes determining a number of DFT precoding units and a size of eachDFT precoding unit. In some cases, determining the DFT configurationincludes determining the DFT configuration based on an MCS, an SNR of atleast one of the set of subcarriers, a phase noise associated with atleast one of the set of subcarriers, a CFO associated with at least oneof the set of subcarriers, or any combination thereof.

DFT component 630 may generate, based on the DFT configuration, a set ofDFT-precoded symbols corresponding to the set of symbols. In some cases,generating the set of DFT-precoded symbols includes generating a firstsubset of the set of DFT-precoded symbols using a first DFT precodingunit. In some cases, generating the set of DFT-precoded symbols includesaccessing a lookup table that associates the set of symbols with the setof DFT-precoded symbols based on the DFT configuration, and retrievingthe set of DFT-precoded symbols from memory.

Mapping component 635 may map the set of DFT-precoded symbols to acorresponding set of subcarriers, the set of subcarriers including atleast a subset of subcarriers that are adjacent in frequency, and maymap additional symbols to additional subcarriers. In some cases, mappingcomponent 635 may map at least one of the additional symbols to asubcarrier within the wireless signal that is interposed in frequencybetween two of the set of subcarriers. In some cases, mapping the set ofDFT-precoded symbols to the set of subcarriers includes mapping thefirst subset of the set of DFT-precoded symbols to the subset ofsubcarriers that are adjacent in frequency. In some cases, mapping theset of DFT-precoded symbols to the set of subcarriers includes mappingsubsets of the set of DFT-precoded symbols to respective subsets of theset of subcarriers, where each subset of the set of DFT-precoded symbolsis associated with a respective DFT precoding unit, and where eachrespective subset of the set of subcarriers includes subcarriers thatare adjacent in frequency.

Transmission component 640 may cause transmitter 620 to transmit the setof DFT-precoded symbols via a wireless signal that includes the set ofsubcarriers and the additional subcarriers.

Transmitter 620 may transmit signals generated by other components ofthe device. In some examples, the transmitter 620 may be collocated witha receiver 610 in a transceiver module. For example, the transmitter 620may be an example of aspects of the transceiver 835 described withreference to FIG. 8. The transmitter 620 may utilize a single antenna ora set of antennas.

FIG. 7 shows a block diagram 700 of a base station communicationsmanager 715 that supports a PT-RS for sub-symbol phase tracking inaccordance with aspects of the present disclosure. The base stationcommunications manager 715 may be an example of aspects of a basestation communications manager 515, a base station communicationsmanager 615, or a base station communications manager 815 described withreference to FIGS. 5, 6, and 8. The base station communications manager715 may include DFT configuration component 720, DFT component 725,mapping component 730, transmission component 735, subcarrier component740, and indication component 745. Each of these modules maycommunicate, directly or indirectly, with one another (e.g., via one ormore buses).

DFT configuration component 720 may determine a DFT configuration for aset of symbols. In some cases, determining the DFT configurationincludes determining a number of DFT precoding units and a size of eachDFT precoding unit. In some cases, determining the DFT configurationincludes determining the DFT configuration based on an MCS, an SNR of atleast one of the set of subcarriers, a phase noise associated with atleast one of the set of subcarriers, a CFO associated with at least oneof the set of subcarriers, or any combination thereof. In some cases,the set of symbols includes a set of PT-RS symbols. In some cases, eachof the set of PT-RS symbols corresponds to a distinct PT-RS sequence.

DFT component 725 may generate, based on the DFT configuration, a set ofDFT-precoded symbols corresponding to the set of symbols. In some cases,generating the set of DFT-precoded symbols includes generating a firstsubset of the set of DFT-precoded symbols using a first DFT precodingunit. In some cases, generating the set of DFT-precoded symbols includesaccessing a lookup table that associates the set of symbols with the setof DFT-precoded symbols based on the DFT configuration, and retrievingthe set of DFT-precoded symbols from memory.

Mapping component 730 may map the set of DFT-precoded symbols to acorresponding set of subcarriers, the set of subcarriers including atleast a subset of subcarriers that are adjacent in frequency, and maymap additional symbols to additional subcarriers. In some cases, mappingcomponent 730 may map at least one of the additional symbols to asubcarrier within the wireless signal that is interposed in frequencybetween two of the set of subcarriers. In some cases, mapping the set ofDFT-precoded symbols to the set of subcarriers includes mapping thefirst subset of the set of DFT-precoded symbols to the subset ofsubcarriers that are adjacent in frequency. In some cases, mapping theset of DFT-precoded symbols to the set of subcarriers includes mappingsubsets of the set of DFT-precoded symbols to respective subsets of theset of subcarriers, where each subset of the set of DFT-precoded symbolsis associated with a respective DFT precoding unit, and where eachrespective subset of the set of subcarriers includes subcarriers thatare adjacent in frequency.

Transmission component 735 may cause a transmitter to transmit the setof DFT-precoded symbols via a wireless signal that includes the set ofsubcarriers and the additional subcarriers.

Subcarrier component 740 may determine the subcarriers to whichDFT-precoded symbols and additional symbols are mapped. For example,subcarrier component 740 may receive, from a wireless device, channelquality information or signals to assist in determining channel qualityinformation, and may determine, based on the channel qualityinformation, at least one of the set of subcarriers. Subcarriercomponent 740 may also receive, from a wireless device, an indication ofone or more preferred subcarriers, and determine, based on theindication, at least one of the set of subcarriers. In some cases, thechannel quality information includes an SNR for at least one of the setof subcarriers.

Indication component 745 may cause a transmitter to transmit anindication of the DFT configuration, an indication of the set ofsubcarriers, or any combination thereof.

FIG. 8 shows a diagram of a system 800 including a device 805 thatsupports a PT-RS for sub-symbol phase tracking in accordance withaspects of the present disclosure. Device 805 may be an example of orinclude the components of wireless device 505, wireless device 605, or abase station 105 as described above, e.g., with reference to FIGS. 5 and6. Device 805 may include components for bi-directional voice and datacommunications including components for transmitting and receivingcommunications, including base station communications manager 815,processor 820, memory 825, software 830, transceiver 835, antenna 840,network communications manager 845, and inter-station communicationsmanager 850. These components may be in electronic communication via oneor more buses (e.g., bus 810). Device 805 may communicate wirelesslywith one or more user equipment (UE)s 115.

Processor 820 may include an intelligent hardware device, (e.g., ageneral-purpose processor, a DSP, a central processing unit (CPU), amicrocontroller, an ASIC, an FPGA, a programmable logic device, adiscrete gate or transistor logic component, a discrete hardwarecomponent, or any combination thereof). In some cases, processor 820 maybe configured to operate a memory array using a memory controller. Inother cases, a memory controller may be integrated into processor 820.Processor 820 may be configured to execute computer-readableinstructions stored in a memory to perform various functions (e.g.,functions or tasks supporting phase tracking reference signal forsub-symbol phase tracking).

Memory 825 may include random access memory (RAM) and read only memory(ROM). The memory 825 may store computer-readable, computer-executablesoftware 830 including instructions that, when executed, cause theprocessor to perform various functions described herein. In some cases,the memory 825 may contain, among other things, a basic input/outputsystem (BIOS) which may control basic hardware or software operationsuch as the interaction with peripheral components or devices.

Software 830 may include code to implement aspects of the presentdisclosure, including code to support a phase tracking reference signalfor sub-symbol phase tracking. Software 830 may be stored in anon-transitory computer-readable medium such as system memory or othermemory. In some cases, the software 830 may not be directly executableby the processor but may cause a computer (e.g., when compiled andexecuted) to perform functions described herein.

Transceiver 835 may communicate bi-directionally, via one or moreantennas, wired, or wireless links as described above. For example, thetransceiver 835 may represent a wireless transceiver and may communicatebi-directionally with another wireless transceiver. The transceiver 835may also include a modem to modulate the packets and provide themodulated packets to the antennas for transmission, and to demodulatepackets received from the antennas.

In some cases, the wireless device may include a single antenna 840.However, in some cases the device may have more than one antenna 840,which may be capable of concurrently transmitting or receiving multiplewireless transmissions.

Network communications manager 845 may manage communications with thecore network (e.g., via one or more wired backhaul links). For example,the network communications manager 845 may manage the transfer of datacommunications for client devices, such as one or more UEs 115.

Inter-station communications manager 850 may manage communications withother base station 105, and may include a controller or scheduler forcontrolling communications with UEs 115 in cooperation with other basestations 105. For example, the inter-station communications manager 850may coordinate scheduling for transmissions to UEs 115 for variousinterference mitigation techniques such as beamforming or jointtransmission. In some examples, inter-station communications manager 850may provide an X2 interface within an Long Term Evolution (LTE)/LTE-Awireless communication network technology to provide communicationbetween base stations 105.

FIG. 9 shows a block diagram 900 of a wireless device 905 that supportsa PT-RS for sub-symbol phase tracking in accordance with aspects of thepresent disclosure. Wireless device 905 may be an example of aspects ofa UE 115 as described herein. Wireless device 905 may include receiver910, UE communications manager 915, and transmitter 920. Wireless device905 may also include a processor. Each of these components may be incommunication with one another (e.g., via one or more buses).

Receiver 910 may receive information such as packets, user data, orcontrol information associated with various information channels (e.g.,control channels, data channels, and information related to phasetracking reference signal for sub-symbol phase tracking, etc.).Information may be passed on to other components of the device. Thereceiver 910 may be an example of aspects of the transceiver 1235described with reference to FIG. 12. The receiver 910 may utilize asingle antenna or a set of antennas.

UE communications manager 915 may be an example of aspects of the UEcommunications manager 1215 described with reference to FIG. 12.

UE communications manager 915 and/or at least some of its varioussub-components may be implemented in hardware, software executed by aprocessor, firmware, or any combination thereof. If implemented insoftware executed by a processor, the functions of the UE communicationsmanager 915 and/or at least some of its various sub-components may beexecuted by a general-purpose processor, a DSP, an ASIC, an FPGA orother programmable logic device, discrete gate or transistor logic,discrete hardware components, or any combination thereof designed toperform the functions described in the present disclosure. The UEcommunications manager 915 and/or at least some of its varioussub-components may be physically located at various positions, includingbeing distributed such that portions of functions are implemented atdifferent physical locations by one or more physical devices. In someexamples, UE communications manager 915 and/or at least some of itsvarious sub-components may be a separate and distinct component inaccordance with various aspects of the present disclosure. In otherexamples, UE communications manager 915 and/or at least some of itsvarious sub-components may be combined with one or more other hardwarecomponents, including but not limited to an I/O component, atransceiver, a network server, another computing device, one or moreother components described in the present disclosure, or a combinationthereof in accordance with various aspects of the present disclosure.

UE communications manager 915 may identify a DFT configuration for a setof DFT-precoded symbols, receive the set of DFT-precoded symbols via acorresponding set of subcarriers within a wireless signal and additionalsymbols via additional subcarriers within the wireless signal, the setof subcarriers including at least a subset of subcarriers that areadjacent in frequency, estimate a phase error based on the set ofDFT-precoded symbols and the DFT configuration, and apply a phasecorrection based on the phase error to the additional symbols.

Transmitter 920 may transmit signals generated by other components ofthe device. In some examples, the transmitter 920 may be collocated witha receiver 910 in a transceiver module. For example, the transmitter 920may be an example of aspects of the transceiver 1235 described withreference to FIG. 12. The transmitter 920 may utilize a single antennaor a set of antennas.

FIG. 10 shows a block diagram 1000 of a wireless device 1005 thatsupports a PT-RS for sub-symbol phase tracking in accordance withaspects of the present disclosure. Wireless device 1005 may be anexample of aspects of a wireless device 905 or a UE 115 as describedwith reference to FIG. 9. Wireless device 1005 may include receiver1010, UE communications manager 1015, and transmitter 1020. Wirelessdevice 1005 may also include a processor. Each of these components maybe in communication with one another (e.g., via one or more buses).

Receiver 1010 may receive information such as packets, user data, orcontrol information associated with various information channels (e.g.,control channels, data channels, and information related to phasetracking reference signal for sub-symbol phase tracking, etc.).Information may be passed on to other components of the device. Thereceiver 1010 may be an example of aspects of the transceiver 1235described with reference to FIG. 12. The receiver 1010 may utilize asingle antenna or a set of antennas.

UE communications manager 1015 may be an example of aspects of the UEcommunications manager 1215 described with reference to FIG. 12. UEcommunications manager 1015 may also include DFT configuration component1025, reception component 1030, phase error component 1035, and phaseerror correction component 1040.

DFT configuration component 1025 may identify a DFT configuration for aset of DFT-precoded symbols. In some cases, identifying the DFTconfiguration includes receiving an indication of a number of DFTprecoding units and a size of each DFT precoding unit. In some cases,DFT configuration component 1025 may cause the transmitter 1020 totransmit an indication of a preferred DFT configuration.

Reception component 1030 may receive the set of DFT-precoded symbols viaa corresponding set of subcarriers within a wireless signal andadditional symbols via additional subcarriers within the wirelesssignal, the set of subcarriers including at least a subset ofsubcarriers that are adjacent in frequency. In some cases, receptioncomponent 1030 may receive at least one of the additional symbols via asubcarrier within the wireless signal that is interposed in frequencybetween two of the set of subcarriers. In some cases, receiving the setof DFT-precoded symbols includes receiving subsets of the set ofDFT-precoded symbols via respective subsets of the set of subcarriers,each subset of the set of DFT-precoded symbols associated with arespective DFT precoding unit, and each respective subset of the set ofsubcarriers including subcarriers that are adjacent in frequency. Insome cases, the set of DFT-precoded symbols correspond to a set of PT-RSsymbols. In some cases, each of the PT-RS symbols corresponds to adistinct PT-RS sequence.

Phase error component 1035 may estimate a phase error based on the setof DFT-precoded symbols and the DFT configuration. In some cases,estimating the phase error includes comparing the set of symbols to acorresponding set of reference symbols in the time domain. In somecases, estimating the phase error further includes computing a phaseerror trajectory for at least one of the set of subcarriers. In somecases, phase error component 1035 may receive an indication of the setof reference symbols.

Phase error correction component 1040 may apply a phase correction basedon the phase error to the additional symbols. Phase error correctioncomponent 1040 may apply the phase correction in either the time domainor the frequency domain.

Transmitter 1020 may transmit signals generated by other components ofthe device. In some examples, the transmitter 1020 may be collocatedwith a receiver 1010 in a transceiver module. For example, thetransmitter 1020 may be an example of aspects of the transceiver 1235described with reference to FIG. 12. The transmitter 1020 may utilize asingle antenna or a set of antennas.

FIG. 11 shows a block diagram 1100 of a UE communications manager 1115that supports a PT-RS for sub-symbol phase tracking in accordance withaspects of the present disclosure. The UE communications manager 1115may be an example of aspects of a UE communications manager 1215described with reference to FIGS. 9, 10, and 12. The UE communicationsmanager 1115 may include DFT configuration component 1120, receptioncomponent 1125, phase error component 1130, phase error correctioncomponent 1135, DFT processing component 1140, and subcarrier component1145. Each of these modules may communicate, directly or indirectly,with one another (e.g., via one or more buses).

DFT configuration component 1120 may identify a DFT configuration for aset of DFT-precoded symbols and transmit an indication of a preferredDFT configuration. In some cases, identifying the DFT configurationincludes receiving an indication of a number of DFT precoding units anda size of each DFT precoding unit.

Reception component 1125 may receive the set of DFT-precoded symbols viaa corresponding set of subcarriers within a wireless signal andadditional symbols via additional subcarriers within the wirelesssignal, the set of subcarriers including at least a subset ofsubcarriers that are adjacent in frequency. In some cases, receptioncomponent 1125 may receive at least one of the additional symbols via asubcarrier within the wireless signal that is interposed in frequencybetween two of the set of subcarriers. In some cases, receiving the setof DFT-precoded symbols includes receiving subsets of the set ofDFT-precoded symbols via respective subsets of the set of subcarriers,each subset of the set of DFT-precoded symbols associated with arespective DFT precoding unit, and each respective subset of the set ofsubcarriers including subcarriers that are adjacent in frequency. Insome cases, the set of DFT-precoded symbols correspond to a set of PT-RSsymbols. In some cases, each of the PT-RS symbols corresponds to adistinct PT-RS sequence.

Phase error component 1130 may estimate a phase error based on the setof DFT-precoded symbols and the DFT configuration. In some cases,estimating the phase error includes comparing the set of symbols to acorresponding set of reference symbols in the time domain. In somecases, phase error component 1130 may receive an indication of the setof reference symbols. In some cases, estimating the phase error furtherincludes computing a phase error trajectory for at least one of the setof subcarriers.

Phase error correction component 1135 may apply a phase correction basedon the phase error to the additional symbols. Phase error correctioncomponent 1135 may apply the phase correction in either the time domainor the frequency domain.

DFT processing component 1140 may process the set of DFT-precodedsymbols based on the DFT configuration to obtain a corresponding set ofsymbols. In some cases, processing the set of DFT-precoded symbolsincludes applying an inverse DFT (IDFT) to the set of DFT-precodedsymbols. In some cases, processing the set of DFT-precoded symbolsincludes accessing a lookup table that associates the set of symbolswith the set of DFT-precoded symbols based on the DFT configuration, andretrieving the set of symbols from memory.

Subcarrier component 1145 may transmit an indication of a preferredsubcarrier, and may receive an indication of the set of subcarriers.Subcarrier component 1145 may determine the preferred subcarrier basedon an SNR.

FIG. 12 shows a diagram of a system 1200 including a device 1205 thatsupports a PT-RS for sub-symbol phase tracking in accordance withaspects of the present disclosure. Device 1205 may be an example of orinclude the components of UE 115 as described above, e.g., withreference to FIG. 1. Device 1205 may include components forbi-directional voice and data communications including components fortransmitting and receiving communications, including UE communicationsmanager 1215, processor 1220, memory 1225, software 1230, transceiver1235, antenna 1240, and I/O controller 1245. These components may be inelectronic communication via one or more buses (e.g., bus 1210). Device1205 may communicate wirelessly with one or more base stations 105.

Processor 1220 may include an intelligent hardware device, (e.g., ageneral-purpose processor, a DSP, a CPU, a microcontroller, an ASIC, anFPGA, a programmable logic device, a discrete gate or transistor logiccomponent, a discrete hardware component, or any combination thereof).In some cases, processor 1220 may be configured to operate a memoryarray using a memory controller. In other cases, a memory controller maybe integrated into processor 1220. Processor 1220 may be configured toexecute computer-readable instructions stored in a memory to performvarious functions (e.g., functions or tasks supporting phase trackingreference signal for sub-symbol phase tracking).

Memory 1225 may include RAM and ROM. The memory 1225 may storecomputer-readable, computer-executable software 1230 includinginstructions that, when executed, cause the processor to perform variousfunctions described herein. In some cases, the memory 1225 may contain,among other things, a BIOS which may control basic hardware or softwareoperation such as the interaction with peripheral components or devices.

Software 1230 may include code to implement aspects of the presentdisclosure, including code to support a phase tracking reference signalfor sub-symbol phase tracking. Software 1230 may be stored in anon-transitory computer-readable medium such as system memory or othermemory. In some cases, the software 1230 may not be directly executableby the processor but may cause a computer (e.g., when compiled andexecuted) to perform functions described herein.

Transceiver 1235 may communicate bi-directionally, via one or moreantennas, wired, or wireless links as described above. For example, thetransceiver 1235 may represent a wireless transceiver and maycommunicate bi-directionally with another wireless transceiver. Thetransceiver 1235 may also include a modem to modulate the packets andprovide the modulated packets to the antennas for transmission, and todemodulate packets received from the antennas.

In some cases, the wireless device may include a single antenna 1240.However, in some cases the device may have more than one antenna 1240,which may be capable of concurrently transmitting or receiving multiplewireless transmissions.

I/O controller 1245 may manage input and output signals for device 1205.I/O controller 1245 may also manage peripherals not integrated intodevice 1205. In some cases, I/O controller 1245 may represent a physicalconnection or port to an external peripheral. In some cases, I/Ocontroller 1245 may utilize an operating system such as iOS®, ANDROID®,MS-DOS®, MS-WINDOWS®, OS/2®, UNIX®, LINUX®, or another known operatingsystem. In other cases, I/O controller 1245 may represent or interactwith a modem, a keyboard, a mouse, a touchscreen, or a similar device.In some cases, I/O controller 1245 may be implemented as part of aprocessor. In some cases, a user may interact with device 1205 via I/Ocontroller 1245 or via hardware components controlled by I/O controller1245.

FIG. 13 shows a flowchart illustrating a method 1300 for phase trackingreference signal for sub-symbol phase tracking in accordance withaspects of the present disclosure. The operations of method 1300 may beimplemented by a base station 105 or its components as described herein.For example, the operations of method 1300 may be performed by a basestation communications manager as described with reference to FIGS. 5through 8. In some examples, a base station 105 may execute a set ofcodes to control the functional elements of the device to perform thefunctions described below. Additionally or alternatively, the basestation 105 may perform aspects of the functions described below usingspecial-purpose hardware. In some examples, the operations of method1300 or other aspects nominally ascribed to a base station 105 hereinmay be performed by any transmitting node (e.g., by a UE 115), which mayinclude structures and components or otherwise support functionsascribed herein to a base station 105.

At 1305 the base station 105 may determine a DFT configuration for aplurality of symbols. The operations of 1305 may be performed accordingto the methods described herein. In certain examples, aspects of theoperations of 1305 may be performed by a DFT configuration component asdescribed with reference to FIGS. 5 through 8.

At 1310 the base station 105 may generate, based at least in part on theDFT configuration, a plurality of DFT-precoded symbols corresponding tothe plurality of symbols. The operations of 1310 may be performedaccording to the methods described herein. In certain examples, aspectsof the operations of 1310 may be performed by a DFT component asdescribed with reference to FIGS. 5 through 8.

At 1315 the base station 105 may map the plurality of DFT-precodedsymbols to a corresponding plurality of subcarriers, the plurality ofsubcarriers including at least a subset of subcarriers that are adjacentin frequency. The operations of 1315 may be performed according to themethods described herein. In certain examples, aspects of the operationsof 1315 may be performed by a mapping component as described withreference to FIGS. 5 through 8.

At 1320 the base station 105 may map additional symbols to additionalsubcarriers. The operations of 1320 may be performed according to themethods described herein. In certain examples, aspects of the operationsof 1320 may be performed by a mapping component as described withreference to FIGS. 5 through 8.

At 1325 the base station 105 may transmit the plurality of DFT-precodedsymbols via a wireless signal that includes the plurality of subcarriersand the additional subcarriers. The operations of 1325 may be performedaccording to the methods described herein. In certain examples, aspectsof the operations of 1325 may be performed by a transmission componentas described with reference to FIGS. 5 through 8.

Aspects of method 1300 may provide for techniques to address identifyingand correcting phase errors at wireless devices. Phase errors in awireless system may be due to various factors including phase noise,carrier frequency offset, or Doppler effect, as a receiver and atransmitter may move relative to one another. To ameliorate theseissues, various techniques at wireless devices may be utilized. Forexample, a base station may frequency division multiplex DFT-precodedsymbols with other symbols and transmit the frequency divisionmultiplexed symbols to a UE. A UE (or other receiving device, such asanother base station) may receive the wireless signal and estimate aphase error based at least in part on the DFT-precoded symbols.

FIG. 14 shows a flowchart illustrating a method 1400 for phase trackingreference signal for sub-symbol phase tracking in accordance withaspects of the present disclosure. The operations of method 1400 may beimplemented by a UE 115 or its components as described herein. Forexample, the operations of method 1400 may be performed by a UEcommunications manager as described with reference to FIGS. 9 through12. In some examples, a UE 115 may execute a set of codes to control thefunctional elements of the device to perform the functions describedbelow. Additionally or alternatively, the UE 115 may perform aspects ofthe functions described below using special-purpose hardware. In someexamples, the operations of method 1400 or other aspects nominallyascribed to a UE 115 herein may be performed by any receiving node(e.g., by a base station 105), which may include structures andcomponents or otherwise support functions ascribed herein to a UE 115.

At 1405 the UE 115 may identify a DFT configuration for a plurality ofDFT-precoded symbols. The operations of 1405 may be performed accordingto the methods described herein. In certain examples, aspects of theoperations of 1405 may be performed by a DFT configuration component asdescribed with reference to FIGS. 9 through 12.

At 1410 the UE 115 may receive the plurality of DFT-precoded symbols viaa corresponding plurality of subcarriers within a wireless signal andadditional symbols via additional subcarriers within the wirelesssignal, the plurality of subcarriers including at least a subset ofsubcarriers that are adjacent in frequency. The operations of 1410 maybe performed according to the methods described herein. In certainexamples, aspects of the operations of 1410 may be performed by areception component as described with reference to FIGS. 9 through 12.

At 1415 the UE 115 may estimate a phase error based at least in part onthe plurality of DFT-precoded symbols and the DFT configuration. Theoperations of 1415 may be performed according to the methods describedherein. In certain examples, aspects of the operations of 1415 may beperformed by a phase error component as described with reference toFIGS. 9 through 12.

At 1420 the UE 115 may apply a phase correction based at least in parton the phase error to the additional symbols. The operations of 1420 maybe performed according to the methods described herein. In certainexamples, aspects of the operations of 1420 may be performed by a phaseerror correction component as described with reference to FIGS. 9through 12.

Aspects of method 1400 may provide for techniques to address identifyingand correcting phase errors at wireless devices. Phase errors in awireless system may be due to various factors including phase noise,carrier frequency offset, or Doppler effect, as a receiver and atransmitter may move relative to one another. To ameliorate theseissues, various techniques at wireless devices may be utilized. Forexample, a base station may frequency division multiplex DFT-precodedsymbols with other symbols and transmit the frequency divisionmultiplexed symbols to a UE. A UE (or other receiving device, such asanother base station) may receive the wireless signal and estimate aphase error based at least in part on the DFT-precoded symbols.

It should be noted that the methods described above describe possibleimplementations, and that the operations and the steps may be rearrangedor otherwise modified and that other implementations are possible.Further, aspects from two or more of the methods may be combined.

Techniques described herein may be used for various wirelesscommunications systems such as code division multiple access (CDMA),time division multiple access (TDMA), frequency division multiple access(FDMA), orthogonal frequency division multiple access (OFDMA), singlecarrier frequency division multiple access (SC-FDMA), and other systems.A CDMA system may implement a radio technology such as CDMA2000,Universal Terrestrial Radio Access (UTRA), etc. CDMA2000 covers IS-2000,IS-95, and IS-856 standards. IS-2000 Releases may be commonly referredto as CDMA2000 1×, 1×, etc. IS-856 (TIA-856) is commonly referred to asCDMA2000 1×EV-DO, High Rate Packet Data (HRPD), etc. UTRA includesWideband CDMA (WCDMA) and other variants of CDMA. A TDMA system mayimplement a radio technology such as Global System for MobileCommunications (GSM).

An OFDMA system may implement a radio technology such as Ultra MobileBroadband (UMB), Evolved UTRA (E-UTRA), Institute of Electrical andElectronics Engineers (IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE802.20, Flash-OFDM, etc. UTRA and E-UTRA are part of Universal MobileTelecommunications System (UMTS). LTE, LTE-A, and LTE-A Pro are releasesof UMTS that use E-UTRA. UTRA, E-UTRA, UMTS, LTE, LTE-A, LTE-A Pro, NR,and GSM are described in documents from the organization named “3rdGeneration Partnership Project” (3GPP). CDMA2000 and UMB are describedin documents from an organization named “3rd Generation PartnershipProject 2” (3GPP2). The techniques described herein may be used for thesystems and radio technologies mentioned above as well as other systemsand radio technologies. While aspects of an LTE, LTE-A, LTE-A Pro, or NRsystem may be described for purposes of example, and LTE, LTE-A, LTE-APro, or NR terminology may be used in much of the description, thetechniques described herein are applicable beyond LTE, LTE-A, LTE-A Pro,or NR applications.

A macro cell generally covers a relatively large geographic area (e.g.,several kilometers in radius) and may allow unrestricted access by UEs115 with service subscriptions with the network provider. A small cellmay be associated with a lower-powered base station 105, as comparedwith a macro cell, and a small cell may operate in the same or different(e.g., licensed, unlicensed, etc.) frequency bands as macro cells. Smallcells may include pico cells, femto cells, and micro cells according tovarious examples. A pico cell, for example, may cover a small geographicarea and may allow unrestricted access by UEs 115 with servicesubscriptions with the network provider. A femto cell may also cover asmall geographic area (e.g., a home) and may provide restricted accessby UEs 115 having an association with the femto cell (e.g., UEs 115 in aclosed subscriber group (CSG), UEs 115 for users in the home, and thelike). An eNB for a macro cell may be referred to as a macro eNB. An eNBfor a small cell may be referred to as a small cell eNB, a pico eNB, afemto eNB, or a home eNB. An eNB may support one or multiple (e.g., two,three, four, and the like) cells, and may also support communicationsusing one or multiple component carriers.

The wireless communications system 100 or systems described herein maysupport synchronous or asynchronous operation. For synchronousoperation, the base stations 105 may have similar frame timing, andtransmissions from different base stations 105 may be approximatelyaligned in time. For asynchronous operation, the base stations 105 mayhave different frame timing, and transmissions from different basestations 105 may not be aligned in time. The techniques described hereinmay be used for either synchronous or asynchronous operations.

Information and signals described herein may be represented using any ofa variety of different technologies and techniques. For example, data,instructions, commands, information, signals, bits, symbols, and chipsthat may be referenced throughout the above description may berepresented by voltages, currents, electromagnetic waves, magneticfields or particles, optical fields or particles, or any combinationthereof.

The various illustrative blocks and modules described in connection withthe disclosure herein may be implemented or performed with ageneral-purpose processor, a digital signal processor (DSP), anapplication-specific integrated circuit (ASIC), a field-programmablegate array (FPGA) or other programmable logic device (PLD), discretegate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general-purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices (e.g., a combinationof a DSP and a microprocessor, multiple microprocessors, one or moremicroprocessors in conjunction with a DSP core, or any other suchconfiguration).

The functions described herein may be implemented in hardware, softwareexecuted by a processor, firmware, or any combination thereof. Ifimplemented in software executed by a processor, the functions may bestored on or transmitted over as one or more instructions or code on acomputer-readable medium. Other examples and implementations are withinthe scope of the disclosure and appended claims. For example, due to thenature of software, functions described above can be implemented usingsoftware executed by a processor, hardware, firmware, hardwiring, orcombinations of any of these. Features implementing functions may alsobe physically located at various positions, including being distributedsuch that portions of functions are implemented at different physicallocations.

Computer-readable media includes both non-transitory computer storagemedia and communication media including any medium that facilitatestransfer of a computer program from one place to another. Anon-transitory storage medium may be any available medium that can beaccessed by a general purpose or special purpose computer. By way ofexample, and not limitation, non-transitory computer-readable media cancomprise RAM, ROM, electrically erasable programmable read only memory(EEPROM), compact disk (CD) ROM or other optical disk storage, magneticdisk storage or other magnetic storage devices, or any othernon-transitory medium that can be used to carry or store desired programcode means in the form of instructions or data structures and that canbe accessed by a general-purpose or special-purpose computer, or ageneral-purpose or special-purpose processor. Also, any connection isproperly termed a computer-readable medium. For example, if the softwareis transmitted from a website, server, or other remote source using acoaxial cable, fiber optic cable, twisted pair, digital subscriber line(DSL), or wireless technologies such as infrared, radio, and microwave,then the coaxial cable, fiber optic cable, twisted pair, DSL, orwireless technologies such as infrared, radio, and microwave areincluded in the definition of medium. Disk and disc, as used herein,include CD, laser disc, optical disc, digital versatile disc (DVD),floppy disk and Blu-ray disc where disks usually reproduce datamagnetically, while discs reproduce data optically with lasers.Combinations of the above are also included within the scope ofcomputer-readable media.

As used herein, including in the claims, “or” as used in a list of items(e.g., a list of items prefaced by a phrase such as “at least one of” or“one or more of”) indicates an inclusive list such that, for example, alist of at least one of A, B, or C means A or B or C or AB or AC or BCor ABC (i.e., A and B and C). Also, as used herein, the phrase “basedon” shall not be construed as a reference to a closed set of conditions.For example, an exemplary step that is described as “based on conditionA” may be based on both a condition A and a condition B withoutdeparting from the scope of the present disclosure. In other words, asused herein, the phrase “based on” shall be construed in the same manneras the phrase “based at least in part on.”

In the appended figures, similar components or features may have thesame reference label. Further, various components of the same type maybe distinguished by following the reference label by a dash and a secondlabel that distinguishes among the similar components. If just the firstreference label is used in the specification, the description isapplicable to any one of the similar components having the same firstreference label irrespective of the second reference label, or othersubsequent reference label.

The description set forth herein, in connection with the appendeddrawings, describes example configurations and does not represent allthe examples that may be implemented or that are within the scope of theclaims. The term “exemplary” used herein means “serving as an example,instance, or illustration,” and not “preferred” or “advantageous overother examples.” The detailed description includes specific details forthe purpose of providing an understanding of the described techniques.These techniques, however, may be practiced without these specificdetails. In some instances, well-known structures and devices are shownin block diagram form in order to avoid obscuring the concepts of thedescribed examples.

The description herein is provided to enable a person skilled in the artto make or use the disclosure. Various modifications to the disclosurewill be readily apparent to those skilled in the art, and the genericprinciples defined herein may be applied to other variations withoutdeparting from the scope of the disclosure. Thus, the disclosure is notlimited to the examples and designs described herein, but is to beaccorded the broadest scope consistent with the principles and novelfeatures disclosed herein.

What is claimed is:
 1. A method for wireless communication, comprising:identifying a discrete Fourier transform (DFT) configuration for aplurality of DFT-precoded symbols; receiving the plurality ofDFT-precoded symbols via a corresponding plurality of subcarriers withina wireless signal and non-DFT precoded symbols via additionalsubcarriers apart from the plurality of subcarriers within the wirelesssignal, the plurality of subcarriers including at least a subset ofsubcarriers that are adjacent in frequency; estimating a phase errorbased at least in part on the plurality of DFT-precoded symbols and theDFT configuration; and applying a phase correction based at least inpart on the phase error to the non-DFT precoded symbols.
 2. The methodof claim 1, further comprising: processing the plurality of DFT-precodedsymbols based at least in part on the DFT configuration to obtain acorresponding plurality of symbols.
 3. The method of claim 2, whereinestimating the phase error comprises: comparing the plurality of symbolsto a corresponding plurality of reference symbols in the time domain. 4.The method of claim 3, further comprising: receiving an indication ofthe plurality of reference symbols.
 5. The method of claim 3, whereinestimating the phase error further comprises: computing a phase errortrajectory for at least one of the plurality of subcarriers.
 6. Themethod of claim 2, wherein processing the plurality of DFT-precodedsymbols comprises: applying an inverse DFT (IDFT) to the plurality ofDFT-precoded symbols.
 7. The method of claim 2, wherein processing theplurality of DFT-precoded symbols comprises: accessing a lookup tablethat associates the plurality of symbols with the plurality ofDFT-precoded symbols based at least in part on the DFT configuration;and retrieving the plurality of symbols from memory.
 8. The method ofclaim 1, further comprising: transmitting an indication of a preferredsubcarrier.
 9. The method of claim 1, further comprising: transmittingan indication of a preferred DFT configuration.
 10. The method of claim1, wherein identifying the DFT configuration comprises: receiving anindication of a number of DFT precoding units and a size of each DFTprecoding unit.
 11. The method of claim 1, further comprising: receivingan indication of the plurality of subcarriers.
 12. The method of claim1, wherein applying the phase correction to the non-DFT precoded symbolsoccurs in either the time domain or the frequency domain.
 13. The methodof claim 1, further comprising: receiving at least one of the non-DFTprecoded symbols via a subcarrier within the wireless signal that isinterposed in frequency between two of the plurality of subcarriers. 14.The method of claim 1, wherein receiving the plurality of DFT-precodedsymbols comprises: receiving subsets of the plurality of DFT-precodedsymbols via respective subsets of the plurality of subcarriers, eachsubset of the plurality of DFT-precoded symbols associated with arespective DFT precoding unit, and each respective subset of theplurality of subcarriers comprising subcarriers that are adjacent infrequency.
 15. The method of claim 1, wherein the plurality ofDFT-precoded symbols correspond to a plurality of phase trackingreference signal (PT-RS) symbols.
 16. The method of claim 15, whereineach of the plurality of PT-RS symbols corresponds to a distinct PT-RSsequence.
 17. An apparatus for wireless communication, comprising: aprocessor; memory coupled to the processor; and instructions stored inthe memory and executable by the processor to cause the apparatus to:identify a discrete Fourier transform (DFT) configuration for aplurality of DFT-precoded symbols; receive the plurality of DFT-precodedsymbols via a corresponding plurality of subcarriers within a wirelesssignal and non-DFT precoded symbols via additional subcarriers apartfrom the plurality of subcarriers within the wireless signal, theplurality of subcarriers including at least a subset of subcarriers thatare adjacent in frequency; estimate a phase error based at least in parton the plurality of DFT-precoded symbols and the DFT configuration; andapply a phase correction based at least in part on the phase error tothe non-DFT precoded symbols.
 18. The apparatus of claim 17, wherein theinstructions are further executable by the processor to cause theapparatus to: process the plurality of DFT-precoded symbols based atleast in part on the DFT configuration to obtain a correspondingplurality of symbols.
 19. The apparatus of claim 18, wherein theinstructions to estimate the phase error are executable by the processorto further cause the apparatus to: compare the plurality of symbols to acorresponding plurality of reference symbols in the time domain.
 20. Theapparatus of claim 19, wherein the instructions are further executableby the processor to cause the apparatus to: receive an indication of theplurality of reference symbols.
 21. The apparatus of claim 19, whereinthe instructions to estimate the phase error are executable by theprocessor to further cause the apparatus to: compute a phase errortrajectory for at least one of the plurality of subcarriers.
 22. Theapparatus of claim 18, wherein the instructions to process the pluralityof DFT-precoded symbols are executable by the processor to further causethe apparatus to: apply an inverse DFT (IDFT) to the plurality ofDFT-precoded symbols.
 23. The apparatus of claim 18, wherein theinstructions to process the plurality of DFT-precoded symbols areexecutable by the processor to further cause the apparatus to: access alookup table that associates the plurality of symbols with the pluralityof DFT-precoded symbols based at least in part on the DFT configuration;and retrieve the plurality of symbols from memory.
 24. The apparatus ofclaim 17, wherein the instructions are further executable by theprocessor to cause the apparatus to: transmit an indication of apreferred DFT configuration.
 25. The apparatus of claim 17, wherein theinstructions to identify the DFT configuration are executable by theprocessor to further cause the apparatus to: receive an indication of anumber of DFT precoding units and a size of each DFT precoding unit. 26.The apparatus of claim 17, wherein the instructions are furtherexecutable by the processor to cause the apparatus to: receive at leastone of the non-DFT precoded symbols via a subcarrier within the wirelesssignal that is interposed in frequency between two of the plurality ofsubcarriers.
 27. The apparatus of claim 17, wherein the instructions toreceive the plurality of DFT-precoded symbols are executable by theprocessor to further cause the apparatus to: receive subsets of theplurality of DFT-precoded symbols via respective subsets of theplurality of subcarriers, each subset of the plurality of DFT-precodedsymbols associated with a respective DFT precoding unit, and eachrespective subset of the plurality of subcarriers comprising subcarriersthat are adjacent in frequency.
 28. The apparatus of claim 17, whereinthe plurality of DFT-precoded symbols correspond to a plurality of phasetracking reference signal (PT-RS) symbols.
 29. An apparatus for wirelesscommunication, comprising: means for identifying a discrete Fouriertransform (DFT) configuration for a plurality of DFT-precoded symbols;means for receiving the plurality of DFT-precoded symbols via acorresponding plurality of subcarriers within a wireless signal andnon-DFT precoded symbols via additional subcarriers apart from theplurality of subcarriers within the wireless signal, the plurality ofsubcarriers including at least a subset of subcarriers that are adjacentin frequency; means for estimating a phase error based at least in parton the plurality of DFT-precoded symbols and the DFT configuration; andmeans for applying a phase correction based at least in part on thephase error to the non-DFT precoded symbols.
 30. A non-transitorycomputer-readable medium storing code for wireless communications, thecode comprising instructions executable by a processor to: identify adiscrete Fourier transform (DFT) configuration for a plurality ofDFT-precoded symbols; receive the plurality of DFT-precoded symbols viaa corresponding plurality of subcarriers within a wireless signal andnon-DFT precoded symbols via additional subcarriers apart from theplurality of subcarriers within the wireless signal, the plurality ofsubcarriers including at least a subset of subcarriers that are adjacentin frequency; estimate a phase error based at least in part on theplurality of DFT-precoded symbols and the DFT configuration; and apply aphase correction based at least in part on the phase error to thenon-DFT precoded symbols.